Support reading and querying Almanac service PHIDs via "diffusion.repository.search"
Ref T13222. See PHI992. If you lose all hosts in a service cluster, you may need to get a list of affected repositories to figure out which backups to pull.
Support doing this via the API.
Test Plan: Queried by service PHID and saw service PHIDs in the call results.
Reviewed By: amckinley
Maniphest Tasks: T13222
Differential Revision: https://secure.phabricator.com/D19848