chore(examples): adds optional tenant-based cookie handling by domain in multi-tenant example (#8490)

- Adds optional tenant-based cookie handling based by domain (commented
out to leave functionality out by default)

- Removes 2.0 multi-tenant example

- Updates `examples/multi-tenant-single-domain` -->
`examples/multi-tenant`

examples/multi-tenant/next.config.mjs

@@ -0,0 +1,8 @@
+import { withPayload } from '@payloadcms/next/withPayload'
+
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  // Your Next.js config here
+}
+
+export default withPayload(nextConfig)