[feature] Push notifications (#3587)

* Update push subscription API model to be Mastodon 4.0 compatible

* Add webpush-go dependency

# Conflicts:
#	go.sum

* Single-row table for storing instance's VAPID key pair

* Generate VAPID key pair during startup

* Add VAPID public key to instance info API

* Return VAPID public key when registering an app

* Store Web Push subscriptions in DB

* Add Web Push sender (similar to email sender)

* Add no-op push senders to most processor tests

* Test Web Push notifications from workers

* Delete Web Push subscriptions when account is deleted

* Implement push subscription API

* Linter fixes

* Update Swagger

* Fix enum to int migration

* Fix GetVAPIDKeyPair

* Create web push subscriptions table with indexes

* Log Web Push server error messages

* Send instance URL as Web Push JWT subject

* Accept any 2xx code as a success

* Fix malformed VAPID sub claim

* Use packed notification flags

* Remove unused date columns

* Add notification type for update notifications

Not used yet

* Make GetVAPIDKeyPair idempotent

and remove PutVAPIDKeyPair

* Post-rebase fixes

* go mod tidy

* Special-case 400 errors other than 408/429

Most client errors should remove the subscription.

* Improve titles, trim body to reasonable length

* Disallow cleartext HTTP for Web Push servers

* Fix lint

* Remove redundant index on unique column

Also removes redundant unique and notnull tags on ID column since these are implied by pk

* Make realsender.go more readable

* Use Tobi's style for wrapping errors

* Restore treating all 5xx codes as temporary problems

* Always load target account settings

* Stub `policy` and `standard`

* webpush.Sender: take type converter as ctor param

* Move webpush.MockSender and noopSender into testrig

1 files changed, 10 insertions, 0 deletions

diff --git a/internal/api/model/instancev2.go b/internal/api/model/instancev2.go
index 982ed0c63..b3d11dee2 100644
--- a/internal/api/model/instancev2.go
+++ b/internal/api/model/instancev2.go
@@ -174,6 +174,8 @@ type InstanceV2Configuration struct {
 	Emojis InstanceConfigurationEmojis `json:"emojis"`
 	// True if instance is running with OIDC as auth/identity backend, else omitted.
 	OIDCEnabled bool `json:"oidc_enabled,omitempty"`
+	// Instance VAPID configuration.
+	VAPID InstanceV2ConfigurationVAPID `json:"vapid"`
 }
 
 // Information about registering for this instance.
@@ -204,3 +206,11 @@ type InstanceV2Contact struct {
 	// Key/value not present if no contact account set.
 	Account *Account `json:"account,omitempty"`
 }
+
+// InstanceV2ConfigurationVAPID holds the instance's VAPID configuration.
+//
+// swagger:model instanceV2ConfigurationVAPID
+type InstanceV2ConfigurationVAPID struct {
+	// The instance's VAPID public key, Base64-encoded.
+	PublicKey string `json:"public_key"`
+}