Move Harbormaster Build Plans to modular transactions

Summary: Depends on D20216. Ref T13258. Bland infrastructure update to prepare for bigger things.

Test Plan: Created and edited a build plan.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13258

Differential Revision: https://secure.phabricator.com/D20217