Create an inital discovery endpoint

[amrc-benmorrow]

Create an endpoint for initial discovery bootstrapping, given nothing but the base cluster domain name.

• This should be accessible without authentication.
• This should provide at least the Directory service URL.
• This should also provide the information needed to build a krb5.conf.

The main traefik configuration then needs adjusting to serve (or redirect to) this endpoint from the base cluster URL. This should only happen for machine access, i.e. with Accept: application/json or something similar. We want to keep the option for human access to be redirected to some human interface, like the Manager.

[amrc-benmorrow]

There is the start of an implementation of this in the acs-admin repo, though this isn't integrated into the ACS monorepo yet.