Mastodon API: Add unsupported attributes to relationship responses

These attributes are documented as required by the Mastodon API.
Since we don’t support them (I think?), respond with default values.

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

@@ -75,8 +75,10 @@ def render("relationship.json", %{user: user, target: target}) do
       followed_by: User.following?(target, user),
       blocking: User.blocks?(user, target),
       muting: false,
+      muting_notifications: false,
       requested: false,
-      domain_blocking: false
+      domain_blocking: false,
+      showing_reblogs: false
     }
   end
 

test/web/mastodon_api/account_view_test.exs

@@ -123,8 +123,10 @@ test "represent a relationship" do
       followed_by: false,
       blocking: true,
       muting: false,
+      muting_notifications: false,
       requested: false,
-      domain_blocking: false
+      domain_blocking: false,
+      showing_reblogs: false
     }
 
     assert expected == AccountView.render("relationship.json", %{user: user, target: other_user})