Modularize Application Email Herald field
Summary:
Ref T8726. There's no interface we can check for this, so the adapter needs to opt in.
Also fix a spelling mistake.
Test Plan: Created rules with "Application Email" fields.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T8726
Differential Revision: https://secure.phabricator.com/D13499