Add federation relay support (#7998)

* Add federation relay support

* Add admin UI for managing relays

* Include actor on relay-related activities

* Fix i18n

app/serializers/activitypub/delete_actor_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class ActivityPub::DeleteActorSerializer < ActiveModel::Serializer
-  attributes :id, :type, :actor
+  attributes :id, :type, :actor, :to
   attribute :virtual_object, key: :object
 
   def id
@@ -19,4 +19,8 @@ class ActivityPub::DeleteActorSerializer < ActiveModel::Serializer
   def virtual_object
     actor
   end
+
+  def to
+    [ActivityPub::TagManager::COLLECTIONS[:public]]
+  end
 end