Automatic merge from submit-queue (batch tested with PRs 49961, 50005, 50738, 51045, 49927)
Add --append-hash flag to kubectl create configmap/secret
**What this PR does / why we need it**:
Specifying this new flag will automatically hash the configmap/secret
contents with sha256 and append the first 40 hex-encoded bits of the
hash to the name of the configmap/secret. This is especially useful for
workflows that generate configmaps/secrets from files (e.g.
--from-file).
See this Google doc for more background:
https://docs.google.com/document/d/1x1fJ3pGRx20ujR-Y89HUAw8glUL8-ygaztLkkmQeCdU/edit
**Release note**:
```release-note
Adds --append-hash flag to kubectl create configmap/secret, which will append a short hash of the configmap/secret contents to the name during creation.
```
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