Expose Build Plan behaviors via "harbormaster.buildplan.search"

Summary: Ref T13258. This will support changing behaviors in "arc land".

Test Plan: Called "harbormaster.buildplan.search", saw behavior information in results.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13258

Differential Revision: https://secure.phabricator.com/D20228