Trivially implement RepositoryEditEngine and API methods

Summary: Ref T10748. Ref T10337. This technically implements this stuff, but it does not do anything useful yet. This skips all the hard stuff.

Test Plan:

• Technically used diffusion.repository.search to get repository information.
• Technically used diffusion.repository.edit to change a repository name.
• Used editpro/ to edit a repository name.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10337, T10748

Differential Revision: https://secure.phabricator.com/D15736