R1:8818252f525c

[herald] Add support for Arcanist Project as a field for Differential revisions

Summary: Useful in cases where there is an Arcanist Project but not a repository tracked by Phabricator for a particular revision.

Test Plan: Created a new rule to flag Differential revisions with a particular Arcanist project, verified that it applied as expected via the test console to revisions with the project specified and with a different project specified.

Reviewers: #blessed_reviewers, epriestley

Reviewed By…