Docs: Documentation on authentication with middleware should mention to exclude server functions

### What is the documentation issue? If inside a middleware someone has such logic: ``` if (isProtectedRoute && !session) { return NextResponse.redirect(new URL("/login", req.nextUrl)); } ``` and if the request comes from server function, this _redirect does not work_ and the _server function which triggered this middleware call is also not called_. Details about this are [here](https://github.com/vercel/next.js/discussions/81608) and [here](https://github.com/vercel/next.js/discussions/64993). Also [here](https://github.com/vercel/next.js/discussions/54753) is another user who stumbled upon this. The solution (from the gh issue above) is to configure the middleware such that it omits server functions. **But this must be said in the docs (maybe [here](https://nextjs.org/docs/app/guides/authentication#optimistic-checks-with-middleware-optional)) otherwise it could lead to bugs.** Actually the example from [docs](https://nextjs.org/docs/app/guides/authentication#optimistic-checks-with-middleware-optional) contains this problematic code. This situation can easily happen when someone is on a protected page, then session expires, and they trigger some (protected) server function. ### Is there any context that might help us understand? [1](https://github.com/vercel/next.js/discussions/81608) ### Does the docs page already exist? Please link to it. https://nextjs.org/docs/app/guides/authentication