Improve @remix-run/serve api

[valotas]

Right now createApp is configured with a bunch of mostly paths needed in order to create an express app/middleware with the right mappings. It would be better to minimize the config provided to the createApp function.

Since all of the paths provided as config can be computed based on the remix.config.js, I would like to propose to have the createApp be able to accept it's path as input (plus process.env.NODE_ENV).

Why the path and not an object of the same type?

Because you can assume that the folder of the path being the root of your remix app. That would make any fixes related to configuration much easier and could be handled in one place. After all the motivation for this change came from #4135

I still like the object approach

In this case it would still be better to share the type import('@remix-run/dev').AppConfig since adding more string arguments to the createApp does not help with it's readability.

Dependencies

If such a solution is ok, @remix-run/serve would need also to share/reuse the code for "reading" the remix.config.js since the default config values should somehow still get computed