Add default View, Edit, and Join Policies to Projects
Summary: Fixes T6567, lets admins set a default policy for new Projects.
Test Plan: Changed the default Policy, created a new Project. Project had correct defaults.
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T6567
Differential Revision: https://secure.phabricator.com/D10890