feat: Adds a webhook for when a user follows the stream (#4362)

* feat: Adds a webhook for when a user follow the stream

Frontend:
Adds a checkbox which renders only when social features are enabled.

Backend:
- Defines a new type for the event
- Implements the webhook including unit testing
- Fires the webhook inside the ApproveFollower handler

* Removes unnecessary Type fiels from Events struct

* refactor: renames SendUserFollowedEvent func to FediverseEngagementFollow and fixes linting errors

* fix: fixes unit test to reflect removed Type field from FediverseEngagementFollowEvent

* feat: fires webhook also when manual approvals are not required

* chore: slight cleanup

---------

Co-authored-by: Gabe Kangas <gabek@real-ity.com>

core/webhooks/fediverseEngagement.go

@@ -0,0 +1,32 @@
+package webhooks
+
+import (
+	"github.com/owncast/owncast/activitypub/events"
+	"github.com/owncast/owncast/activitypub/persistence"
+	"github.com/owncast/owncast/models"
+)
+
+// SendFediverseEventFollow will send a user followed event to webhook
+// destinations.
+func SendFediverseEngagementFollowEvent(iri string) {
+	follower, err := persistence.GetFollower(iri)
+	if err != nil {
+		return
+	}
+	userFollowedEvent := events.FediverseEngagementFollowEvent{}
+	userFollowedEvent.SetDefaults()
+	userFollowedEvent.Name = follower.Name
+	userFollowedEvent.Username = follower.Username
+	userFollowedEvent.Image = follower.Image.String()
+
+	sendFediverseEngagementEventFollow(userFollowedEvent)
+}
+
+func sendFediverseEngagementEventFollow(event events.FediverseEngagementFollowEvent) {
+	webhookEvent := WebhookEvent{
+		Type:      models.FediverseEngagementFollow,
+		EventData: event,
+	}
+
+	SendEventToWebhooks(webhookEvent)
+}