R1:5bbf0ba13256

Add a setup warning about deprecated Maniphest policy configuration

Summary: Ref T10003. Give installs more warning about these changes.

Test Plan: Changed configuration, saw warning. Reset configuration, no warning.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10003

Differential Revision: https://secure.phabricator.com/D14817