R1:a542024b6334

Update Phortune subscriptions for modern infrastructure

Summary:
Depends on D20720. Ref T13366.

- 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.

Subscribers: PHID…