Check Notifications center configuration compliance

Summary:
The Notifications center now publish a configuration report,
per f3fcf394ac9c.

That allows us to compare the production config with a reference one.

Fixes T663.

Test Plan: New test checked against https://notifications.nasqueron.org/config

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T663

Differential Revision: https://devcentral.nasqueron.org/D791