Automatic merge from submit-queue (batch tested with PRs 63526, 60371, 63444). 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>.
Support completion for kubectl cp
**What this PR does / why we need it**: With this PR, kubectl cp supports completion. I tested this PR in bash and zsh.
```
$ kubectl cp kube-system/<tab>
kube-system/kube-state-metrics-769566fdfb-4v52s: kube-system/kubernetes-dashboard-6b6ddbd46-t5bv9: kube-system/prometheus-694594c45b-qk5lq:
```
**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/kubectl#5
**Special notes for your reviewer**: @cblecker
**Release note**:
```release-note
`kubectl cp` supports completion.
```
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