feat(server): disable 404 response

[deer]

closes https://github.com/denoland/fresh/issues/1918

@harrysolovay, what do you think of this? This change allows you to do something like this:

export default defineConfig({
  router: {
    disabled404response: () => {
      throw new Error("my custom error");
    },
  },
});

or

export default defineConfig({
  router: {
    disabled404response: () => {
      return new Response("asdf");
    },
  },
});

I can look to see what it would take to allow just returning undefined, but that seems like a larger change.

[deer]

No feedback from the requester, so I'll just mark this as ready and see what happens. I'm totally open to reworking this, if desired.

[harrysolovay]

Apologies I haven't had time to give an appropriate review. TBH I don't believe I'd be the right reviewer. Not familiar with the codebase.

[deer]

@harrysolovay, sorry for the miscommunication. All I was looking for was whether the interface of the config is acceptable to you. I know you were hoping for returning undefined, but I thought perhaps a configurable function allowing you to return whatever error you want would possibly be acceptable.

[harrysolovay]

I suppose it's an improvement over needing to create a dedicated 404 route file. Still, I believe getting back a Response | undefined from the render fn would be preferable.