Automatic merge from submit-queue
Support persisting config from kubecfg AuthProvider plugins
Plumbs through an interface to the plugin that can persist a `map[string]string` config for just that plugin. Also adds `config` to the AuthProvider serialization type, and `Login()` to the AuthProvider plugin interface.
Modified the gcp AuthProvider to cache short-term access tokens in the kubecfg file.
Builds on #23066
@bobbyrullo @deads2k @jlowdermilk @erictune
f40fe7173b