Expose Audit actions for "transaction.search" in a basic way

Summary: Ref T13210. See PHI841. This mirrors D19509 for Differential.

Test Plan: Called transaction.search on a commit with a bunch of audit activity, got appropriate labels in the results.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13210

Differential Revision: https://secure.phabricator.com/D19760