chore(examples): removes external auth examples (#8605)

In effort to keep the Examples Directory as easy to navigate as
possible, and to keep the Payload Monorepo only as verbose as it needs
to be, we need to remove all alternatives from the Examples Directory.
This includes setups that interact with Payload from a standalone
server, keeping only the Payload recommended "combined" Next.js +
Payload setups. This will also be applied to all other examples that use
this setup, i.e. draft preview, live preview, etc.

examples/auth/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)