Allow repositories to be bound to an AlmanacService

Summary:
Ref T2783. This is primarily exploratory and just figuring out what we're blocked on:

• Allow a Repository to be bound to a Service. The Service may eventually define multiple read/write nodes, etc.
  • There's no UI to do this binding yet, you have to touch the database manually.
• If a repository is bound to a Service, effect Conduit calls via calls to the remote service instead of executing them in-process.
  • These don't actually work yet since there's no authentication (see T5955).

Test Plan:

• Made a nice Service with a nice Binding to a nice Interface on a nice Device.
• Force-associated a repository with the service using a raw MySQL query.
• Saw Phabricator try to make a remote call to the service (on localhost) and fail because of missing auth stuff.
• Also ran almanac.queryservices.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2783

Differential Revision: https://secure.phabricator.com/D10982