Add conduit.getcapabilities and a modern CLI handshake workflow

Summary:
Ref T5955.

  - Add `conduit.getcapabilities` to help arc (and other clients) determine formats, protocols, etc., the server supports.
  - Fixes T3117. Add a more modern version of the handshake workflow that allows all generated tokens to remain valid for an hour.
  - Generally, add a CLI token type. This token type expires after an hour when generated, then becomes permanent if used.

Test Plan:
  - See D10988.
  - Ran `conduit.getcapabilities` and inspected output.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T3117, T5955

Differential Revision: https://secure.phabricator.com/D10989