✨ Add describeServer lexicon for ozone

[foysalit]

This PR introduces a new tools.ozone.server.describeServer route to fetch info about ozone instance. As of now, it exposes the moderators with their role/access level.

[bnewbold]

Just to clarify, we won't make the set of moderators public and enumerable. If we do have an endpoint to enumerate them, requiring auth, it should have a different name to avoid confusion with com.atproto.server.describeServer, which is public.

[foysalit]

yep, this enpoint is authed so not exposing anything publicly.
makes sense to change it from describeServer but I was hoping this will be a generic endpoint that will fetch all the server level config and not just the moderator list so it kinda made sense from that angle.
until we have proper user management, a dedicated endpoint just for exposing the moderator list feels a bit "extra" especially because the current list is configured through env var.

[devinivy]

I think the user only needs to know their own access level, so perhaps the full list could just be boiled down to the requesting user's access level.

[foysalit]

Closing this in favor of #2460 which handles moderator ACL management and will create a separate PR for exposing server configs only.