R1:8d8ee18ce0fd

Modularize Maniphest Herald "Assign Task" action

Summary: Ref T8726. No surprises here.

Test Plan:
- Created rules using this action.
- Applied migration.
- Verified rules still work.

{F659324}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: joshuaspence, epriestley

Maniphest Tasks: T8726

Differential Revision: https://secure.phabricator.com/D13706