Pass optional connector_id to cluster_context

[corest]

My use-case is:

• dex with two connectors, e.g. github with id "id1" and Microsoft with id "id2"
• two dex-k8s-authenticator apps:
  • /login/app1 -> this should call dex with github connector
  • /login/app2 -> this should call dex with microsoft connector
    The goal is to skip dex login page where you need to choose your connector.

With this change, I can configure my separate dex-k8s-authenticator apps with connector_id: id1 and connector_id: i2 respectively for cluster context. Then visiting a separate authenticator app will point me directly to a specified connector

[nabadger]

Nice, I didn't know this option existed in Dex :)