Allow Conduit API methods in Diffusion to accept any repository identifier

Summary:
Ref T4245. Broaden support to include "ABCD", "rABCD", "1234", "R1234", etc.

This doesn't change the old behavior, just accepts more stuff.

Test Plan:

• Browsed Diffusion.
• Made various calls via API console.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14928