Merge branch 'jnnkl-eventlistener-clusters-index' into 'master'

Remove obsolete DOMContentLoadedEventListener

See merge request gitlab-org/gitlab!53968

app/assets/javascripts/pages/projects/clusters/index/index.js

 import initClustersListApp from 'ee_else_ce/clusters_list';
 import PersistentUserCallout from '~/persistent_user_callout';
 
-document.addEventListener('DOMContentLoaded', () => {
-  const callout = document.querySelector('.gcp-signup-offer');
-  PersistentUserCallout.factory(callout);
-  initClustersListApp();
-});
+const callout = document.querySelector('.gcp-signup-offer');
+PersistentUserCallout.factory(callout);
+initClustersListApp();