Add shared inbox support for ActivityPub delivery (#4755)

* feat(ap): add support for shared inboxes to reduce outbound load

* feat(db): refactor ap followers db into followers repository

* fix(ap): use the updated activity library to pull out the shared inbox endpoint

* chore(deps): point at updated build of owncast/activity

* fix(ap): typeless endpoints

* feat(test): update ActivityPub test to support shared inboxes

* chore(test): remove unused variable

* fix: feedback from review. Guard against SSRF/non-HTTPS/local and handle transaction errors

core/webhooks/fediverseEngagement.go

@@ -2,14 +2,15 @@ package webhooks
 
 import (
 	"github.com/owncast/owncast/activitypub/events"
-	"github.com/owncast/owncast/activitypub/persistence"
+	"github.com/owncast/owncast/activitypub/persistence/followersrepository"
 	"github.com/owncast/owncast/models"
 )
 
 // SendFediverseEventFollow will send a user followed event to webhook
 // destinations.
 func SendFediverseEngagementFollowEvent(iri string) {
-	follower, err := persistence.GetFollower(iri)
+	followersRepo := followersrepository.Get()
+	follower, err := followersRepo.GetByIRI(iri)
 	if err != nil {
 		return
 	}