Add "localOnly" property to created AP notes

Useful for third party clients doing feature detection.

app/serializers/activitypub/note_serializer.rb

@@ -9,7 +9,7 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
              :in_reply_to, :published, :url,
              :attributed_to, :to, :cc, :sensitive,
              :atom_uri, :in_reply_to_atom_uri,
-             :conversation
+             :conversation, :local_only
 
   attribute :content
   attribute :content_map, if: :language?
@@ -108,6 +108,10 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
     object.account.sensitized? || object.sensitive
   end
 
+  def local_only
+    object.local_only
+  end
+
   def virtual_attachments
     object.ordered_media_attachments
   end