Receive most overseer configuration over stdin

Summary: Ref T7352. Change overseers to read configuration in a JSON blob over stdin, and possibly run multiple daemons (for now, they don't actually do this).

Test Plan: Ran phd debug, phd launch, phd status, etc. Some of the status stuff is a little bit rough for now until it can get cleaned up.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7352

Differential Revision: https://secure.phabricator.com/D11854