Summary:
- Reading plans from Stripe, and allowing Stripe to define custom plans.
- Storing product features (aka limits) in Stripe, that override those in db.
- Adding hierarchical data in Stripe. All features are defined at Product level but can be overwritten on Price levels.
- New options for Support user to
-- Override product for team site (if he is added as a billing manager)
-- Override subscription and customer id for a team site
-- Attach an "offer", an custom plan configured in stripe that a team site can use
-- Enabling wire transfer for subscription by allowing subscription to be created without a payment method (which is customizable)
Test Plan: Updated and new.
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D4201
