Add basic Herald support to Ponder

Summary: Ref T6919, Just a basic herald adapter (new questions) for Ponder

Test Plan: Created a Personal Rule, got subscribed to new question, saw transcript.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T6919

Differential Revision: https://secure.phabricator.com/D13828