Add modern "Accept", "Raise Concern" and "Resign" transactions to Audit

Summary:
Ref T10978. This prepares for swapping the comment UI to stacked actions.

These are only accessible via the API.

Test Plan: Used the API to accept, raise concern with, and reject commits.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10978

Differential Revision: https://secure.phabricator.com/D17182