Merge branch 'ce-billings-gold-trial-callout' into 'master'

CE BE Prep backend for /billings gold trial callouts

See merge request gitlab-org/gitlab-ce!25482

app/helpers/user_callouts_helper.rb

@@ -17,6 +17,9 @@ module UserCalloutsHelper
     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)