EE port for 29398 support kubernetes rbac for gitlab managed apps

CE MR at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21127

What does this MR do?

EE port for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21127

• Implement rbac? for UpgradeCommand which is now required by BaseCommand
• Update a concern used by both KubernetesService and Clusters::Platforms::Kubernetes to use build_kube_client! as build_kubeclient! no longer exists

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/29398

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• [-] For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?

Manual QA

• Check that UpgradeCommand works in a RBAC cluster
• Check that UpgradeCommand works in a ABAC cluster
  • provision a new cluster with GitLab on master
  • install prometheus
  • switch to this branch, restart GDK
  • trigger UpgradeCommand by setting up an alert on a custom metric

To trigger UpgradeCommand, use the steps from https://gitlab.com/gitlab-org/gitlab-ce/issues/47154#note_92205407, then check the cluster on GKE