Automatic merge from submit-queue. 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>.

staging: add boilerplate header

Follow up of https://github.com/kubernetes/kubernetes/pull/57656.

Adds boilerplate in the relevant staging repos so that they don't need to depend on code-generator's boilerplate.

**Release note**:

```release-note
NONE
```

/cc sttts fisherxu