Is your feature request related to a problem? Please describe.

By default k0s configures only cert based auth for API server and only the admin.conf with cluster admin role bound to it.

We should make available some subcommand to easily create a new cert and kubeconfig for a new user.

Describe the solution you'd like
k0s user create jussi --group foo,bar

That would dump out a kubeconfig with embedded certs for a user called jussi. In the cert there's groups for foo and bar.

Describe alternatives you've considered

Additional context