Prep backend for /billings gold trial callouts

Ports GoldTrialUserCallouts to CE.

app/helpers/user_callouts_helper.rb

@@ -17,6 +17,9 @@ def render_flash_user_callout(flash_type, message, feature_name)
     render 'shared/flash_user_callout', flash_type: flash_type, message: message, feature_name: feature_name
   end
 
+  def render_dashboard_gold_trial(user)
+  end
+
   private
 
   def user_dismissed?(feature_name)