Automatic merge from submit-queue

kubectl config set-crentials: add arguments for auth providers

This PR adds `--auth-provider` and `--auth-provider-arg` flags to the
`kubectl config set-credentials` sub-command.

There's currently no way of interacting with the new auth provider framework added in #23066 through kubectl. You have to render a custom kubeconfig to use them. Additionally `kubectl config set` just sort of craps out when attempting to interact with authentication info objects (#29312).

This is a minimal implementation of allowing `kubect config set-credentials` to set fields for client auth providers.

cc @cjcullen @kubernetes/kubectl