Support oauth tokens for auth

[joemiller]

It would be great if this plugin supported OAuth tokens for authenticating to the cluster. This would allow for easy usage by GKE-hosted clusters in particular since Google recommends disabling both basic-auth and cert-auth in their hardening guide.

Example of token support in the standard TF k8s provider - https://www.terraform.io/docs/providers/google/d/datasource_client_config.html#example-usage-configure-kubernetes-provider-with-oauth2-access-token