Add a "did verify email" event to Phabricator

Summary: Ref T7152. Gives us an event hook so we can go make users a member of any instance they've been invited to as soon as they verify an email address.

Test Plan:

• Used bin/auth verify to trigger the event.
• Build out the invite flow in rSERVICES.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7152

Differential Revision: https://secure.phabricator.com/D11752