(core) Billing for formula assistant

Summary:
Adding limits for AI calls and connecting those limits with a Stripe Account.

- New table in homedb called `limits`
- All calls to the AI are not routed through DocApi and measured.
- All products now contain a special key `assistantLimit`, with a default value 0
- Limit is reset every time the subscription has changed its period
- The billing page is updated with two new options that describe the AI plan
- There is a new popup that allows the user to upgrade to a higher plan
- Tiers are read directly from the Stripe product with a volume pricing model

Test Plan: Updated and added

Reviewers: georgegevoian, paulfitz

Reviewed By: georgegevoian

Subscribers: dsagal

Differential Revision: https://phab.getgrist.com/D3907

app/client/models/NotifyModel.ts

@@ -43,8 +43,8 @@ export interface CustomAction { label: string, action: () => void }
  */
 export type MessageType = string | (() => DomElementArg);
 // Identifies supported actions. These are implemented in NotifyUI.
-export type NotifyAction = 'upgrade' | 'renew' | 'personal' | 'report-problem' | 'ask-for-help' | CustomAction;
-
+export type NotifyAction = 'upgrade' | 'renew' | 'personal' | 'report-problem'
+                           | 'ask-for-help' | 'manage' | CustomAction;
 export interface INotifyOptions {
   message: MessageType;     // A string, or a function that builds dom.
   timestamp?: number;

app/client/models/errors.ts

@@ -121,7 +121,7 @@ export function reportError(err: Error|string, ev?: ErrorEvent): void {
       const options: Partial<INotifyOptions> = {
         title: "Reached plan limit",
         key: `limit:${details.limit.quantity || message}`,
-        actions: ['upgrade'],
+        actions: details.tips?.some(t => t.action === 'manage') ? ['manage'] : ['upgrade'],
       };
       if (details.tips && details.tips.some(tip => tip.action === 'add-members')) {
         // When adding members would fix a problem, give more specific advice.