Move Conduit client construction logic into Repository

Summary: Ref T7020. I need this elsewhere, and it's relatively internal anyway.

Test Plan: Browsed around my local, cluster-configured install and saw everything working fine.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7020

Differential Revision: https://secure.phabricator.com/D11474