enhancement(with-supabase): replace getSession() with getUser() (#61564)
### What?
Enhancement of _with-supabase example_. Replacing in **middelware.ts**,
**supabase.auth.getSession()** with **supabase.auth.getUser()**
### Why?
**Never trust supabase.auth.getSession() inside server code such as
middleware**. It isn't guaranteed to revalidate the Auth token.
**It's safe to trust getUser()** because it sends a request to the
Supabase Auth server every time to revalidate the Auth token.
[Setting up Server-Side Auth for
Next.js](https://supabase.com/docs/guides/auth/server-side/nextjs)