Add callout priority enum

app/helpers/callouts_helper.rb

 module CalloutsHelper
   GKE_CLUSTER_INTEGRATION = 'gke_cluster_integration'.freeze
 
+  # Higher value = higher priority
+  PRIORITY = {
+    GKE_CLUSTER_INTEGRATION: 0
+  }.freeze
+
   def show_gke_cluster_integration_callout?(project)
     current_user && !user_dismissed?(GKE_CLUSTER_INTEGRATION) &&
       (project.team.master?(current_user) ||