Expose transaction PHID in maniphest.gettasktransactions
Summary: Fixes T6629.
Test Plan: {F238271}
Reviewers: btrahan, chad, 20after4
Reviewed By: 20after4
Subscribers: 20after4, epriestley
Maniphest Tasks: T6629
Differential Revision: https://secure.phabricator.com/D10898