Modularize HarbormasterBuildTransaction

Summary: Ref T13072. Update "HarbormasterBuild" to use modern modular transactions.

Test Plan:

• Aborted, restarted, paused, and resumed a build.
• Used bin/harbormaster restart.
• Grepped for use of old "::TYPE_COMMAND" constant, didn't find any hits.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13072

Differential Revision: https://secure.phabricator.com/D21689