Automatic merge from submit-queue (batch tested with PRs 41216, 41362, 41275, 41277, 41412)
kubeadm: test-cmd: join{config, discovery}
**What this PR does / why we need it**: Adding test-cmds for kubeadm join {config, discovery}. Will followup with more test-cmds for other flags as soon as validation for the flags works.
Adding tests is a WIP from #34136
**Special notes for your reviewer**: /cc @luxas @pires
**Release note**:
```release-note
NONE
```