[cern] k8s_fedora: Add admin user

Spyridon Trigazis requested to merge OS-6474-k8s-add-admin-user into cern-queens

cherry-pick: https://review.openstack.org/#/c/563679/ jira: OS-6474

Add an admin service account and give it the cluster role. It can be used for access apps with token authentication like the kubernetes-dashboard.

Remove the cluster role from the dashboard service account.

Change-Id: I7980c0e72b0d71921e42af7338d02b8a1e563c34 Closes-Bug: #1766284 (cherry picked from commit 91d5229b)

Closes OS-6474

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