Add encoding information to "repository.query"

Summary: Ref T7604. Add encoding information to the repository.query #conduit query.

Test Plan: Changed repository encoding from the UI and saw the encoding returned by the Conduit call.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7604

Differential Revision: https://secure.phabricator.com/D12992