Automatic merge from submit-queue (batch tested with PRs 39694, 39383, 39651, 39691, 39497)

Add support for groups to passwordfile

As we move deployment methods to using RBAC, it is useful to be able to place the admin user in the bootstrap kubeconfig files in a superuser group. The tokencsv file supports specifying group membership, but the basicauth file does not. This adds it for parity.

I plan to update the generated password file to put the admin user in a group (similar to the way https://github.com/kubernetes/kubernetes/pull/39537 puts that user in a group in the token file)

```release-note
--basic-auth-file supports optionally specifying groups in the fourth column of the file
```