Apps: add user_id index

priv/repo/migrations/20210818023112_add_user_id_to_apps.exs

@@ -5,5 +5,7 @@ def change do
     alter table(:apps) do
       add(:user_id, references(:users, type: :uuid, on_delete: :delete_all))
     end
+
+    create_if_not_exists(index(:apps, [:user_id]))
   end
 end