Automatic merge from submit-queue (batch tested with PRs 51039, 50512, 50546, 50965, 50467)
Kubectl: Plumb openapi validation (disabled by default)
**What this PR does / why we need it**: Creates a new flag '--openapi' and plumb in the validation code so that it can be used by default to validate objects against the openapi schema.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: partially https://github.com/kubernetes/kubectl/issues/49
**Special notes for your reviewer**:
This is not complete, the name of the variable must change for example.
**Release note**:
```release-note
Kubectl uses openapi for validation. If OpenAPI is not available on the server, it defaults back to the old Swagger.
```
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