Do not hardcode default Priority names in Project Reports tooltip

Summary:
Pull the names of Priority field values instead of hardcoding them.

Closes T15799

Test Plan:

• As an admin, go to /config/edit/maniphest.priorities/ and change the value of "name" of a Priority value with a value < 50 (e.g.: Low, Wishlist)
• Open /maniphest/report/project/
• Hover over the Oldest (Pri) column and check the tooltip text before and after applying this patch

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15799

Differential Revision: https://we.phorge.it/D25602