Add repositories to Diviner
Summary: Fixes T8352. Associate Diviner books and atoms with a repository. This relationship is not really surfaced anywhere in the UI but provides metadata that contextualises search results. Depends on D13091.
Test Plan: Ran diviner generate --repository ARC and then went to /diviner/book/arcanist/.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D13070