(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

test/formula-dataset/runCompletion_impl.ts

@@ -25,7 +25,7 @@
 
 
 import { ActiveDoc, Deps as ActiveDocDeps } from "app/server/lib/ActiveDoc";
-import { DEPS } from "app/server/lib/Assistance";
+import { DEPS, sendForCompletion } from "app/server/lib/Assistance";
 import log from 'app/server/lib/log';
 import crypto from 'crypto';
 import parse from 'csv-parse/lib/sync';
@@ -163,7 +163,7 @@ where c.colId = ? and t.tableId = ?
 `, rec.col_id, rec.table_id);
           formula = colInfo?.formula;
 
-          const result = await activeDoc.getAssistanceWithOptions(session, {
+          const result = await sendForCompletion(session, activeDoc, {
             context: {type: 'formula', tableId, colId},
             state: history,
             text: followUp || description,