R1:a07a8aca2462

Add a daemon overseer module to restart daemons when config changes

Summary: Fixes T7053. Depends on D14452.

Test Plan:
Created a custom daemon which dumps out the config hash (by querying `PhabricatorEnv::calculateEnvironmentHash()`). Ran this daemon with `./bin/phd debug PhabricatorDebugDaemon` and saw the config hash update within 30 seconds.

{P1886}

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T7053

Differential…