Automatic merge from submit-queue (batch tested with PRs 64318, 64269, 64438, 64516, 64311). 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>.
UX improvement for preflight check for external etcd client certificates
**What this PR does / why we need it**:
UX improvement for preflight check for external etcd client certificates
By using same preflight check label for all etcd client certificates, it will
allow user to use single identifier, and as result shorter command line
arguments to kubeadm, in case multiple issues found with those files.
Fixes:
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixeskubernetes/kubeadm#834
**Special notes for your reviewer**:
**Release note**:
```release-note
Label ExternalEtcdClientCertificates can be used for ignoring all preflight check issues related to client certificate files for external etcd.
```
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