[chore] Simplify the OTEL setup (#4110)

# Description

This simplifies our OTEL setup by:

* Getting rid of some deprecated things.
* Using `autoexport` and letting things get configured by the `OTEL_` environment variables.
* Removing all the unnecessary config options.

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [ ] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4110
Reviewed-by: tobi <kipvandenbos@noreply.codeberg.org>
Co-authored-by: Daenney <daenney@noreply.codeberg.org>
Co-committed-by: Daenney <daenney@noreply.codeberg.org>

3 files changed, 4 insertions, 167 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 88083d491..2c4035ecf 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -145,16 +145,8 @@ type Configuration struct {
 	OIDCLinkExisting     bool     `name:"oidc-link-existing" usage:"link existing user accounts to OIDC logins based on the stored email value"`
 	OIDCAllowedGroups    []string `name:"oidc-allowed-groups" usage:"Membership of one of the listed groups allows access to GtS. If this is empty, all groups are allowed."`
 	OIDCAdminGroups      []string `name:"oidc-admin-groups" usage:"Membership of one of the listed groups makes someone a GtS admin"`
-
-	TracingEnabled           bool   `name:"tracing-enabled" usage:"Enable OTLP Tracing"`
-	TracingTransport         string `name:"tracing-transport" usage:"grpc or http"`
-	TracingEndpoint          string `name:"tracing-endpoint" usage:"Endpoint of your trace collector. Eg., 'localhost:4317' for gRPC, 'localhost:4318' for http"`
-	TracingInsecureTransport bool   `name:"tracing-insecure-transport" usage:"Disable TLS for the gRPC or HTTP transport protocol"`
-
-	MetricsEnabled      bool   `name:"metrics-enabled" usage:"Enable OpenTelemetry based metrics support."`
-	MetricsAuthEnabled  bool   `name:"metrics-auth-enabled" usage:"Enable HTTP Basic Authentication for Prometheus metrics endpoint"`
-	MetricsAuthUsername string `name:"metrics-auth-username" usage:"Username for Prometheus metrics endpoint"`
-	MetricsAuthPassword string `name:"metrics-auth-password" usage:"Password for Prometheus metrics endpoint"`
+	TracingEnabled       bool     `name:"tracing-enabled" usage:"Enable OTLP Tracing"`
+	MetricsEnabled       bool     `name:"metrics-enabled" usage:"Enable OpenTelemetry based metrics support."`
 
 	SMTPHost               string `name:"smtp-host" usage:"Host of the smtp server. Eg., 'smtp.eu.mailgun.org'"`
 	SMTPPort               int    `name:"smtp-port" usage:"Port of the smtp server. Eg., 587"`
diff --git a/internal/config/defaults.go b/internal/config/defaults.go
index 4ef183aa6..7e1d234f3 100644
--- a/internal/config/defaults.go
+++ b/internal/config/defaults.go
@@ -122,13 +122,8 @@ var Defaults = Configuration{
 	SMTPFrom:               "",
 	SMTPDiscloseRecipients: false,
 
-	TracingEnabled:           false,
-	TracingTransport:         "grpc",
-	TracingEndpoint:          "",
-	TracingInsecureTransport: false,
-
-	MetricsEnabled:     false,
-	MetricsAuthEnabled: false,
+	TracingEnabled: false,
+	MetricsEnabled: false,
 
 	SyslogEnabled:  false,
 	SyslogProtocol: "udp",
diff --git a/internal/config/helpers.gen.go b/internal/config/helpers.gen.go
index 8fc4475b7..b039d26a5 100644
--- a/internal/config/helpers.gen.go
+++ b/internal/config/helpers.gen.go
@@ -2306,81 +2306,6 @@ func GetTracingEnabled() bool { return global.GetTracingEnabled() }
 // SetTracingEnabled safely sets the value for global configuration 'TracingEnabled' field
 func SetTracingEnabled(v bool) { global.SetTracingEnabled(v) }
 
-// GetTracingTransport safely fetches the Configuration value for state's 'TracingTransport' field
-func (st *ConfigState) GetTracingTransport() (v string) {
-	st.mutex.RLock()
-	v = st.config.TracingTransport
-	st.mutex.RUnlock()
-	return
-}
-
-// SetTracingTransport safely sets the Configuration value for state's 'TracingTransport' field
-func (st *ConfigState) SetTracingTransport(v string) {
-	st.mutex.Lock()
-	defer st.mutex.Unlock()
-	st.config.TracingTransport = v
-	st.reloadToViper()
-}
-
-// TracingTransportFlag returns the flag name for the 'TracingTransport' field
-func TracingTransportFlag() string { return "tracing-transport" }
-
-// GetTracingTransport safely fetches the value for global configuration 'TracingTransport' field
-func GetTracingTransport() string { return global.GetTracingTransport() }
-
-// SetTracingTransport safely sets the value for global configuration 'TracingTransport' field
-func SetTracingTransport(v string) { global.SetTracingTransport(v) }
-
-// GetTracingEndpoint safely fetches the Configuration value for state's 'TracingEndpoint' field
-func (st *ConfigState) GetTracingEndpoint() (v string) {
-	st.mutex.RLock()
-	v = st.config.TracingEndpoint
-	st.mutex.RUnlock()
-	return
-}
-
-// SetTracingEndpoint safely sets the Configuration value for state's 'TracingEndpoint' field
-func (st *ConfigState) SetTracingEndpoint(v string) {
-	st.mutex.Lock()
-	defer st.mutex.Unlock()
-	st.config.TracingEndpoint = v
-	st.reloadToViper()
-}
-
-// TracingEndpointFlag returns the flag name for the 'TracingEndpoint' field
-func TracingEndpointFlag() string { return "tracing-endpoint" }
-
-// GetTracingEndpoint safely fetches the value for global configuration 'TracingEndpoint' field
-func GetTracingEndpoint() string { return global.GetTracingEndpoint() }
-
-// SetTracingEndpoint safely sets the value for global configuration 'TracingEndpoint' field
-func SetTracingEndpoint(v string) { global.SetTracingEndpoint(v) }
-
-// GetTracingInsecureTransport safely fetches the Configuration value for state's 'TracingInsecureTransport' field
-func (st *ConfigState) GetTracingInsecureTransport() (v bool) {
-	st.mutex.RLock()
-	v = st.config.TracingInsecureTransport
-	st.mutex.RUnlock()
-	return
-}
-
-// SetTracingInsecureTransport safely sets the Configuration value for state's 'TracingInsecureTransport' field
-func (st *ConfigState) SetTracingInsecureTransport(v bool) {
-	st.mutex.Lock()
-	defer st.mutex.Unlock()
-	st.config.TracingInsecureTransport = v
-	st.reloadToViper()
-}
-
-// TracingInsecureTransportFlag returns the flag name for the 'TracingInsecureTransport' field
-func TracingInsecureTransportFlag() string { return "tracing-insecure-transport" }
-
-// GetTracingInsecureTransport safely fetches the value for global configuration 'TracingInsecureTransport' field
-func GetTracingInsecureTransport() bool { return global.GetTracingInsecureTransport() }
-
-// SetTracingInsecureTransport safely sets the value for global configuration 'TracingInsecureTransport' field
-func SetTracingInsecureTransport(v bool) { global.SetTracingInsecureTransport(v) }
-
 // GetMetricsEnabled safely fetches the Configuration value for state's 'MetricsEnabled' field
 func (st *ConfigState) GetMetricsEnabled() (v bool) {
 	st.mutex.RLock()
@@ -2406,81 +2331,6 @@ func GetMetricsEnabled() bool { return global.GetMetricsEnabled() }
 // SetMetricsEnabled safely sets the value for global configuration 'MetricsEnabled' field
 func SetMetricsEnabled(v bool) { global.SetMetricsEnabled(v) }
 
-// GetMetricsAuthEnabled safely fetches the Configuration value for state's 'MetricsAuthEnabled' field
-func (st *ConfigState) GetMetricsAuthEnabled() (v bool) {
-	st.mutex.RLock()
-	v = st.config.MetricsAuthEnabled
-	st.mutex.RUnlock()
-	return
-}
-
-// SetMetricsAuthEnabled safely sets the Configuration value for state's 'MetricsAuthEnabled' field
-func (st *ConfigState) SetMetricsAuthEnabled(v bool) {
-	st.mutex.Lock()
-	defer st.mutex.Unlock()
-	st.config.MetricsAuthEnabled = v
-	st.reloadToViper()
-}
-
-// MetricsAuthEnabledFlag returns the flag name for the 'MetricsAuthEnabled' field
-func MetricsAuthEnabledFlag() string { return "metrics-auth-enabled" }
-
-// GetMetricsAuthEnabled safely fetches the value for global configuration 'MetricsAuthEnabled' field
-func GetMetricsAuthEnabled() bool { return global.GetMetricsAuthEnabled() }
-
-// SetMetricsAuthEnabled safely sets the value for global configuration 'MetricsAuthEnabled' field
-func SetMetricsAuthEnabled(v bool) { global.SetMetricsAuthEnabled(v) }
-
-// GetMetricsAuthUsername safely fetches the Configuration value for state's 'MetricsAuthUsername' field
-func (st *ConfigState) GetMetricsAuthUsername() (v string) {
-	st.mutex.RLock()
-	v = st.config.MetricsAuthUsername
-	st.mutex.RUnlock()
-	return
-}
-
-// SetMetricsAuthUsername safely sets the Configuration value for state's 'MetricsAuthUsername' field
-func (st *ConfigState) SetMetricsAuthUsername(v string) {
-	st.mutex.Lock()
-	defer st.mutex.Unlock()
-	st.config.MetricsAuthUsername = v
-	st.reloadToViper()
-}
-
-// MetricsAuthUsernameFlag returns the flag name for the 'MetricsAuthUsername' field
-func MetricsAuthUsernameFlag() string { return "metrics-auth-username" }
-
-// GetMetricsAuthUsername safely fetches the value for global configuration 'MetricsAuthUsername' field
-func GetMetricsAuthUsername() string { return global.GetMetricsAuthUsername() }
-
-// SetMetricsAuthUsername safely sets the value for global configuration 'MetricsAuthUsername' field
-func SetMetricsAuthUsername(v string) { global.SetMetricsAuthUsername(v) }
-
-// GetMetricsAuthPassword safely fetches the Configuration value for state's 'MetricsAuthPassword' field
-func (st *ConfigState) GetMetricsAuthPassword() (v string) {
-	st.mutex.RLock()
-	v = st.config.MetricsAuthPassword
-	st.mutex.RUnlock()
-	return
-}
-
-// SetMetricsAuthPassword safely sets the Configuration value for state's 'MetricsAuthPassword' field
-func (st *ConfigState) SetMetricsAuthPassword(v string) {
-	st.mutex.Lock()
-	defer st.mutex.Unlock()
-	st.config.MetricsAuthPassword = v
-	st.reloadToViper()
-}
-
-// MetricsAuthPasswordFlag returns the flag name for the 'MetricsAuthPassword' field
-func MetricsAuthPasswordFlag() string { return "metrics-auth-password" }
-
-// GetMetricsAuthPassword safely fetches the value for global configuration 'MetricsAuthPassword' field
-func GetMetricsAuthPassword() string { return global.GetMetricsAuthPassword() }
-
-// SetMetricsAuthPassword safely sets the value for global configuration 'MetricsAuthPassword' field
-func SetMetricsAuthPassword(v string) { global.SetMetricsAuthPassword(v) }
-
 // GetSMTPHost safely fetches the Configuration value for state's 'SMTPHost' field
 func (st *ConfigState) GetSMTPHost() (v string) {
 	st.mutex.RLock()