Automatic merge from submit-queue (batch tested with PRs 62444, 66358, 66724, 66726). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Move kubelet serving cert rotation to beta
xref https://github.com/kubernetes/features/issues/267
This is exercised in the alpha gke e2es, and can be enabled in the non-alpha gke e2es once it no longer requires an alpha feature gate.
```release-note
Kubelet serving certificate bootstrapping and rotation has been promoted to beta status.
```
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