Add Operator Console SSO to docs

[feorlen]

New instructions for Operator Console SSO using OpenID are in https://github.com/minio/operator/tree/master/examples/kustomization/operator-external-idp-oid

This makes SSO possible for Operator Console, although there is further work required to make it easy to use. Document the process, along with a recommendation to create a different OIDC realm to limit access to Operator Console.

See minio/operator#1949