Automatic merge from submit-queue (batch tested with PRs 66225, 66648, 65799, 66630, 66619). 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>.
Percent-encode illegal characters in user.Info.Extra keys
This percent-encodes characters in `X-Remote-Extra-` and `Impersonate-Extra-` keys which aren't valid for header names per [RFC 7230](https://tools.ietf.org/html/rfc7230#section-3.2.6) (plus "%" to avoid breaking keys which contain them). The API server then blindly unescapes these keys.
Reviewer note:
Old clients sending keys which were `%`-escaped by the user will have their values unescaped by new API servers. New clients sending keys containing illegal characters (or "%") to old API servers will not have their values unescaped. This version skew incompatibility is a compromise discussed in #63682.
Fixes#63682
PTAL @mikedanese
**Release note**:
```release-note
action required: the API server and client-go libraries have been fixed to support additional non-alpha-numeric characters in UserInfo "extra" data keys. Both should be updated in order to properly support extra data containing "/" characters or other characters disallowed in HTTP headers.
```
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