Config - add phd.variant-config to suppress "Daemon & Web config" error message on a per key basis

Summary: Fixes T6959.

Test Plan: When I was ready to test the feature, the "Daemon & Web config" error already showed up, from having added phd.variant-config. I went meta and changed the value of phd.variant-config to have phd.variant-config. The config error disappeared. I then changed the conpherence setting about conpherence email prefix and the error showed up again. Removing the conpherence config setting made the error disappear once more.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6959

Differential Revision: https://secure.phabricator.com/D11399