Automatic merge from submit-queue (batch tested with PRs 42969, 42966)
kubeadm: update kubeadm banner to beta
**What this PR does / why we need it**: Updates the intro banner for kubeadm, which used to state it is in alpha (but we are going to beta). This also updates the tagged github group (one that no longer exists) to the sig-cluster-lifecycle-misc group.
**Special notes for your reviewer**: /cc @jbeda
**Release note**:
```release-note
NONE
```
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