Automate authentication setup via new auth command

[thomasjo]

Once Frink v2 ships, we should simplify the getting started workflow by implementing automated authentication setup via a new auth command.

Ideally we should no longer be relying on kubectl being installed. If not installed, and no kubeconfig file is found, we should create this file and then configure clusters, users, context, etc. We might need to validate any existing config.

We should also consider adding support for multiple contexts primarily to simplify devops workflows that requires an admin context and what not. Long term multi-context support should make it easier for users to collaborate across namespaces.