Automatic merge from submit-queue (batch tested with PRs 53228, 53232, 53353). 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>.
Openapi explain
**What this PR does / why we need it**:
This rewrites `kubectl explain` but using openapi rather than swagger 1.2. Also removes the former code.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes#49465, fixes partially #44589, fixes partially #38637
**Special notes for your reviewer**:
FYI @mbohlool
**Release note**:
```release-note
`kubectl explain` now uses openapi rather than swagger 1.2.
```
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