Update custom server examples

[timneutkens]

Fixes the links/readme descriptions, also removes legacy routing that can now be handled using rewrites which also work client-side automatically.

Closes #24607

Bug

• Related issues linked using fixes #number
• Integration tests added

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.

Documentation / Examples

• Make sure the linting passes

[cseas]

As someone trying to understand how the Next.js custom Express setup works, I have some questions:

If the server.get() path handlers are not needed here, does that mean the server.all() handler will just know how to handle all the paths defined in pages? So I'm assuming we can just define API endpoints here that Express needs to handle and all the application path routing will just work.

If yes, then what's the point of all the app.render in the documentation example? Shouldn't that only be done when file-system routing is disabled? Having it in the basic example makes it look like it's necessary to define all the path handlers.

I'm also confused about what the query parameter is and how and when it is supposed to be used. In the lines deleted here, we were using req.query and that worked fine. But the documentation example shows that query should be taken from the result of parse(req.url, true) and then passed to the app.render. Can't find any explanation of what query parameter is exactly supposed to be and why does app.render need it.

[cseas]

For context, my use case is that we have a fat Express server serving the build folder from create-react-app. Trying to figure out how to migrate to Next.js to do server-rendering.

I'd expect the documentation/examples to have a mention of:

• Where do the express middlewares fit here?
• Is it necessary to define path handlers for every route of the application?
• Where are the response headers supposed to be in a custom server with Next.js? Will express keep handling the headers for every page request or will Next.js headers override that functionality? Are there any conflicts between the two?

Understandably, these questions could be directed to Discussions or StackOverflow but it'd be great if it's possible to figure these answers out from the documentation.