(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/gen-server/migration/1685343047786-AssistantLimit.ts

@@ -0,0 +1,82 @@
+import * as sqlUtils from "app/gen-server/sqlUtils";
+import {MigrationInterface, QueryRunner, Table, TableIndex} from 'typeorm';
+
+export class AssistantLimit1685343047786 implements MigrationInterface {
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    const dbType = queryRunner.connection.driver.options.type;
+    const datetime = sqlUtils.datetime(dbType);
+    const now = sqlUtils.now(dbType);
+    await queryRunner.createTable(
+      new Table({
+        name: 'limits',
+        columns: [
+          {
+            name: 'id',
+            type: 'integer',
+            isPrimary: true,
+            isGenerated: true,
+            generationStrategy: 'increment',
+          },
+          {
+            name: 'type',
+            type: 'varchar',
+          },
+          {
+            name: 'billing_account_id',
+            type: 'integer',
+          },
+          {
+            name: 'limit',
+            type: 'integer',
+            default: 0,
+          },
+          {
+            name: 'usage',
+            type: 'integer',
+            default: 0,
+          },
+          {
+            name: "created_at",
+            type: datetime,
+            default: now
+          },
+          {
+            name: "changed_at", // When the limit was last changed
+            type: datetime,
+            isNullable: true
+          },
+          {
+            name: "used_at", // When the usage was last increased
+            type: datetime,
+            isNullable: true
+          },
+          {
+            name: "reset_at", // When the usage was last reset.
+            type: datetime,
+            isNullable: true
+          },
+        ],
+        foreignKeys: [
+          {
+            columnNames: ['billing_account_id'],
+            referencedTableName: 'billing_accounts',
+            referencedColumnNames: ['id'],
+            onDelete: 'CASCADE',
+          },
+        ],
+      })
+    );
+
+    await queryRunner.createIndex(
+      'limits',
+      new TableIndex({
+        name: 'limits_billing_account_id',
+        columnNames: ['billing_account_id'],
+      })
+    );
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.dropTable('limits');
+  }
+}