Automatic merge from submit-queue
Fix handling lists in kubectl convert
Fixes https://github.com/kubernetes/kubernetes/issues/36722
When handling multiple objects in `kubectl convert` (for example in `kubectl convert -f .` with multiple files in current directory) the objects must be managed as a list instead of individually, otherwise `-o yaml|json` will generate invalid format (just multiple json/yaml objects concatenated) which can't be fed to `kubectl create` like in `kubectl convert -f . | kubectl create -f -`.
```release-note
NONE
```
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