Audit - add ability to query by repositories

Summary: Fixes T5862. The Diffusion table uses `id` but all the other infrastructure uses `phid` so just do a quick load of the repositories to get the ids. Long term, we should re-key the table by phid I think.

Test Plan: made a query with a repository and got a proper result set

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5862

Differential Revision: https://secure.phabricator.com/D10245