Update Phortune subscriptions for modern infrastructure
- Use modern policies and policy interfaces.
- Use new merchant authority cache.
- Add (some) transactions.
- Move MFA from pre-upgrade-gate to post-one-shot-check.
- Simplify the autopay workflow.
- Use the "reloading arrows" icon for subscriptions more consistently.
Test Plan: As a merchant-authority and account-authority, viewed, edited, and changed autopay for subscriptions.
Maniphest Tasks: T13366
Differential Revision: https://secure.phabricator.com/D20721