feat: update Prisma schema (#9099)

### Description

`referentialIntegrity = "prisma"` is deprecated, the latest feature is
`relationMode = "prisma"`.
Also since `"referentialIntegrity"` is deprecated, preview feature
functionality can be used without specifying it.

### Testing Instructions

Didn't do any testing steps, i just saw this warning as i'm setting up
my own monorepo and decided to update your example aswell. (should not
mess anything up, based on https://pris.ly/d/relation-mode)

examples/with-prisma/packages/database/prisma/schema.prisma

@@ -4,12 +4,11 @@
 datasource db {
   provider = "mysql"
   url      = env("DATABASE_URL")
-  referentialIntegrity = "prisma"
+  relationMode = "prisma"
 }
 
 generator client {
   provider = "prisma-client-js"
-  previewFeatures = ["referentialIntegrity"]
 }
 
 model User {