When adding an exist Kubernetes cluster, the user has the ability to tell us whether the cluster is RBAC enabled or not:  The user must mark this correctly or else there will be errors. We should either: * A) Detect whether the cluster is RBAC enabled so the user is not able to choose incorrectly and remove this checkmark when adding an existing cluster * B) Allow the user to change whether or not the cluster is RBAC enabled when adding an existing cluster. Related: https://gitlab.com/gitlab-org/gitlab-ce/issues/54728