(core) Customizable stripe plans.

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

app/client/widgets/FormulaAssistant.ts

@@ -381,7 +381,7 @@ export class FormulaAssistant extends Disposable {
       canUpgradeSite ? t('upgrade to the Pro Team plan') : t('upgrade your plan'),
       dom.on('click', async () => {
         if (canUpgradeSite) {
-          this._gristDoc.appModel.showUpgradeModal();
+          this._gristDoc.appModel.showUpgradeModal().catch(reportError);
         } else {
           await urlState().pushUrl({billing: 'billing'});
         }