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>

activitypub/events/events.go

@@ -0,0 +1,19 @@
+package events
+
+import (
+	"time"
+
+	"github.com/teris-io/shortid"
+)
+
+// Event is any kind of event.
+type Event struct {
+	Timestamp time.Time `json:"timestamp"`
+	ID        string    `json:"id"`
+}
+
+// SetDefaults will set default properties of all inbound events.
+func (e *Event) SetDefaults() {
+	e.ID = shortid.MustGenerate()
+	e.Timestamp = time.Now()
+}