Automatic merge from submit-queue (batch tested with PRs 63453, 64592, 64482, 64618, 64661). 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: promote exec plugin support to beta
/sig auth
/kind feature
Adds a "v1beta1" API group for client authentication. Because of a lack of usage with the input parameters, these have been dropped for the beta. Would like to re-introduce them as users feel they require them.
updates https://github.com/kubernetes/kubernetes/issues/61796
```release-note
client-go: credential exec plugins have been promoted to beta
```
Kubernetes-commit: 819d51567f82c27ba3b7cde5b4cb3bb59c0550b6
