feat: add multi subscription support (#734)

## Description

Previously we assumed that there can only be 1 subscription per user.
However, that will soon no longer the case with the introduction of the
Teams subscription.

This PR will apply the required migrations to support multiple
subscriptions.

## Changes Made

- Updated the Prisma schema to allow for multiple `Subscriptions` per
`User`
- Added a Stripe `customerId` field to the `User` model
- Updated relevant billing sections to support multiple subscriptions

## Testing Performed

- Tested running the Prisma migration on a demo database created on the
main branch

Will require a lot of additional testing.

## Checklist

- [ ] I have tested these changes locally and they work as expected.
- [ ] I have added/updated tests that prove the effectiveness of these
changes.
- [X] I have followed the project's coding style guidelines.

## Additional Notes

Added the following custom SQL statement to the migration:

> DELETE FROM "Subscription" WHERE "planId" IS NULL OR "priceId" IS
NULL;

Prior to deployment this will require changes to Stripe products:
- Adding `type` meta attribute

---------

Co-authored-by: Lucas Smith <me@lucasjamessmith.me>

packages/ee/server-only/stripe/webhook/handler.ts

@@ -75,23 +75,23 @@ export const stripeWebhookHandler = async (
 
         // Finally, attempt to get the user ID from the subscription within the database.
         if (!userId && customerId) {
-          const result = await prisma.subscription.findFirst({
+          const result = await prisma.user.findFirst({
             select: {
-              userId: true,
+              id: true,
             },
             where: {
               customerId,
             },
           });
 
-          if (!result?.userId) {
+          if (!result?.id) {
             return res.status(500).json({
               success: false,
               message: 'User not found',
             });
           }
 
-          userId = result.userId;
+          userId = result.id;
         }
 
         const subscriptionId =
@@ -124,23 +124,23 @@ export const stripeWebhookHandler = async (
             ? subscription.customer
             : subscription.customer.id;
 
-        const result = await prisma.subscription.findFirst({
+        const result = await prisma.user.findFirst({
           select: {
-            userId: true,
+            id: true,
           },
           where: {
             customerId,
           },
         });
 
-        if (!result?.userId) {
+        if (!result?.id) {
           return res.status(500).json({
             success: false,
             message: 'User not found',
           });
         }
 
-        await onSubscriptionUpdated({ userId: result.userId, subscription });
+        await onSubscriptionUpdated({ userId: result.id, subscription });
 
         return res.status(200).json({
           success: true,
@@ -182,23 +182,23 @@ export const stripeWebhookHandler = async (
           });
         }
 
-        const result = await prisma.subscription.findFirst({
+        const result = await prisma.user.findFirst({
           select: {
-            userId: true,
+            id: true,
           },
           where: {
             customerId,
           },
         });
 
-        if (!result?.userId) {
+        if (!result?.id) {
           return res.status(500).json({
             success: false,
             message: 'User not found',
           });
         }
 
-        await onSubscriptionUpdated({ userId: result.userId, subscription });
+        await onSubscriptionUpdated({ userId: result.id, subscription });
 
         return res.status(200).json({
           success: true,
@@ -233,23 +233,23 @@ export const stripeWebhookHandler = async (
           });
         }
 
-        const result = await prisma.subscription.findFirst({
+        const result = await prisma.user.findFirst({
           select: {
-            userId: true,
+            id: true,
           },
           where: {
             customerId,
           },
         });
 
-        if (!result?.userId) {
+        if (!result?.id) {
           return res.status(500).json({
             success: false,
             message: 'User not found',
           });
         }
 
-        await onSubscriptionUpdated({ userId: result.userId, subscription });
+        await onSubscriptionUpdated({ userId: result.id, subscription });
 
         return res.status(200).json({
           success: true,