Automatic merge from submit-queue

TLS bootstrap API group (alpha)

This PR only covers the new types and related client/storage code- the vast majority of the line count is codegen. The implementation differs slightly from the current proposal document based on discussions in design thread (#20439). The controller logic and kubelet support mentioned in the proposal are forthcoming in separate requests.

I submit that #18762 ("Creating a new API group is really hard") is, if anything, understating it. I've tried to structure the commits to illustrate the process.

@mikedanese @erictune @smarterclayton @deads2k

```release-note-experimental
An alpha implementation of the the TLS bootstrap API described in docs/proposals/kubelet-tls-bootstrap.md.
```

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