docs: move drizzle example to supabase (#45935)

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES/NO

## What kind of change does this PR introduce?

Bug fix, feature, docs update, ...

## What is the current behavior?

Please link any relevant issues here.

## What is the new behavior?

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## Additional context

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## Summary by CodeRabbit

* **Documentation**
* Updated the Drizzle ORM guide to a Deno-native configuration,
replacing the prior import-map example with embedded Deno examples and
references to Edge Function samples.

* **New Features**
* Added an Edge Function example demonstrating Drizzle + PostgreSQL on
Deno.
* Added a shared database schema example including user and countries
table definitions.

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---------

Co-authored-by: Chris Chinchilla <chris.ward@supabase.io>

examples/edge-functions/supabase/functions/_shared/schema.ts

@@ -0,0 +1,16 @@
+import { pgTable, serial, text, timestamp } from 'drizzle-orm/pg-core'
+
+export const user = pgTable('user', {
+  id: serial('id'),
+  name: text('name'),
+  email: text('email'),
+  password: text('password'),
+  role: text('role').$type<'admin' | 'customer'>(),
+  createdAt: timestamp('created_at'),
+  updatedAt: timestamp('updated_at'),
+})
+
+export const countries = pgTable('countries', {
+  id: serial('id'),
+  name: text('name'),
+})

examples/edge-functions/supabase/functions/drizzle/deno.json

@@ -0,0 +1,7 @@
+{
+  "imports": {
+    "drizzle-orm": "npm:drizzle-orm@0.29.1",
+    "drizzle-orm/": "npm:/drizzle-orm@0.29.1/",
+    "postgres": "npm:postgres@3.4.3"
+  }
+}

examples/edge-functions/supabase/functions/drizzle/index.ts

@@ -0,0 +1,14 @@
+import { drizzle } from 'drizzle-orm/postgres-js'
+import postgres from 'postgres'
+import { countries } from '../_shared/schema.ts'
+
+const connectionString = Deno.env.get('SUPABASE_DB_URL')!
+// Disable prefetch as it is not supported for "Transaction" pool mode
+const client = postgres(connectionString, { prepare: false })
+const db = drizzle(client)
+
+Deno.serve(async (_req) => {
+  const allCountries = await db.select().from(countries)
+
+  return Response.json(allCountries)
+})