[feature] Initial Prometheus metrics implementation (#2334)

* feat: Initial OTEL metrics

* docs: add metrics documentation

* fix: metrics endpoint conditional check

* feat: metrics endpoint basic auth

* fix: make metrics-auth-enabled default false

* fix: go fmt helpers.gen.go

* fix: add metric-related env vars to envparsing.sh

* fix: metrics docs

* fix: metrics related stuff in envparsing.sh

* fix: metrics docs

* chore: metrics docs wording

* fix: metrics stuff in envparsing?

* bump otel versions

---------

Co-authored-by: Tsuribori <user@acertaindebian>
Co-authored-by: Tsuribori <none@example.org>
Co-authored-by: tsmethurst <tobi.smethurst@protonmail.com>

3 files changed, 108 insertions, 0 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index b7d2eff36..173999b53 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -140,6 +140,11 @@ type Configuration struct {
 	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"`
+
 	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"`
 	SMTPUsername           string `name:"smtp-username" usage:"Username to authenticate with the smtp server as. Eg., 'postmaster@mail.example.org'"`
diff --git a/internal/config/defaults.go b/internal/config/defaults.go
index 3da489501..5aba6c689 100644
--- a/internal/config/defaults.go
+++ b/internal/config/defaults.go
@@ -121,6 +121,9 @@ var Defaults = Configuration{
 	TracingEndpoint:          "",
 	TracingInsecureTransport: false,
 
+	MetricsEnabled:     false,
+	MetricsAuthEnabled: false,
+
 	SyslogEnabled:  false,
 	SyslogProtocol: "udp",
 	SyslogAddress:  "localhost:514",
diff --git a/internal/config/helpers.gen.go b/internal/config/helpers.gen.go
index a008092d3..393a1b1e9 100644
--- a/internal/config/helpers.gen.go
+++ b/internal/config/helpers.gen.go
@@ -2100,6 +2100,106 @@ func GetTracingInsecureTransport() bool { return global.GetTracingInsecureTransp
 // 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()
+	v = st.config.MetricsEnabled
+	st.mutex.RUnlock()
+	return
+}
+
+// SetMetricsEnabled safely sets the Configuration value for state's 'MetricsEnabled' field
+func (st *ConfigState) SetMetricsEnabled(v bool) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.MetricsEnabled = v
+	st.reloadToViper()
+}
+
+// MetricsEnabledFlag returns the flag name for the 'MetricsEnabled' field
+func MetricsEnabledFlag() string { return "metrics-enabled" }
+
+// GetMetricsEnabled safely fetches the value for global configuration 'MetricsEnabled' field
+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()