Consolidate prometheus into kubernetes application [2/3]

[mikkeloscar]

Follow up to #4900

This is the second of a 3-step change to migrate prometheus statefulset to be a component of kubernetes instead of individual an application.

1. Label the pod spec with statefulset: prometheus, roll out to all clusters.
2. Change the selector to use the label statefulset: prometheus and use the deletions.yaml with propagation_policy: Orphan to delete the old statefulset (without deleting the pods) and create a new statefulset with the new selector.
3. Change the pod template labels for application.

[mikkeloscar]

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[szuecs]

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