People: add a permalink to list Administrators

Summary:
This change introduces a builting query to easily list
Administrators of your beautiful Phorge instance:

{F277912}

Note that any builtin query can be disabled anytime or
reordered, so this is not a problem if you already have
a similar saved query. But probably you have not.

The goal is not to just "have a link" (this was already
possible) but to have a predictable link to be used in
any instance-agnostic document, including but not
limited to Diviner or Phorge's user interface messages.

Closes T15238

Test Plan: Visit /people/query/admin/ and enjoy.

Reviewers: O1 Blessed Committers, Cigaryno, Matthew

Reviewed By: O1 Blessed Committers, Cigaryno, Matthew

Subscribers: speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15238

Differential Revision: https://we.phorge.it/D25116