⚡ (billing) Automatic usage-based billing (#924)

BREAKING CHANGE: Stripe environment variables simplified. Check out the
new configs to adapt your existing system.

Closes #906





<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
### Summary by CodeRabbit

**New Features:**
- Introduced a usage-based billing system, providing more flexibility
and options for users.
- Integrated with Stripe for a smoother and more secure payment process.
- Enhanced the user interface with improvements to the billing,
workspace, and pricing pages for a more intuitive experience.

**Improvements:**
- Simplified the billing logic, removing additional chats and yearly
billing for a more streamlined user experience.
- Updated email notifications to keep users informed about their usage
and limits.
- Improved pricing and currency formatting for better clarity and
understanding.

**Testing:**
- Updated tests and specifications to ensure the reliability of new
features and improvements.

**Note:** These changes aim to provide a more flexible and user-friendly
billing system, with clearer pricing and improved notifications. Users
should find the new system more intuitive and easier to navigate.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/builder/src/test/utils/databaseActions.ts

@@ -18,7 +18,7 @@ const stripe = new Stripe(env.STRIPE_SECRET_KEY ?? '', {
 export const addSubscriptionToWorkspace = async (
   workspaceId: string,
   items: Stripe.SubscriptionCreateParams.Item[],
-  metadata: Pick<Workspace, 'additionalChatsIndex' | 'plan'>
+  metadata: Pick<Workspace, 'plan'>
 ) => {
   const { id: stripeId } = await stripe.customers.create({
     email: 'test-user@gmail.com',