Merge pull request #59495 from ericchiang/client-auth-exec

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>.

 client-go: add an exec-based client auth provider

Updates kubernetes/enhancements#541
Implements kubernetes/community#1503
Closes kubernetes/kubernetes#57164

```release-note
client-go: alpha support for exec-based credential providers
```

/sig auth
/kind feature

Kubernetes-commit: cb9d6b51556a1677f262e35e4aded0051c424818