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