Enable `assumeImmutableResults` on the cluster Agent List

This commit solves https://gitlab.com/gitlab-org/gitlab/-/issues/338563
It enables `assumeImmutableResults` on the cluster Agent List.

ee/app/assets/javascripts/clusters_list/load_agents.js

@@ -8,7 +8,7 @@ export default (Vue, VueApollo) => {
     return null;
   }
 
-  const defaultClient = createDefaultClient();
+  const defaultClient = createDefaultClient({}, { assumeImmutableResults: true });
 
   const {
     emptyStateImage,