Show bubble_timeline in the api if any instances are set in it, do not show if none are set

lib/pleroma/web/mastodon_api/views/instance_view.ex

@@ -67,6 +67,9 @@ def features do
       "pleroma:api/v1/notifications:include_types_filter",
       "quote_posting",
       "editing",
+      if Config.get([:instance, :local_bubble], []) != [] do
+        "bubble_timeline"
+      end,
       if Config.get([:media_proxy, :enabled]) do
         "media_proxy"
       end,