Automatic merge from submit-queue (batch tested with PRs 61354, 61366, 61386, 61394, 60755). 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>.
pkg/printers: Support base64 decode in kubectl get go-template
**What this PR does / why we need it**:
Adds a `base64decode` function to templates in `kubectl` so that it's possible to extract secret data in plaintext instead of base64 without requiring a separate executable to do the decode.
Sample usage:
```sh
kubectl get secret SECRET -o go-template='{{ .data.KEY | base64decode }}'
```
**Which issue(s) this PR fixes**:
Fixeskubernetes/kubernetes#45293.
**Special notes for your reviewer**:
**Release note**:
```release-note
You can now use the `base64decode` function in kubectl go templates to decode base64-encoded data, for example `kubectl get secret SECRET -o go-template='{{ .data.KEY | base64decode }}'`.
```
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