Allow the .server and .client to work outside appDirectory

[chrisfitz]

As it stands today, the .server and .client convention only works within the appDirectory (see here), however this is quite limiting if you're working within a monorepo-style repository or have some code lives outside the appDirectory.

Consider the Following

app/
build/
public/
node_modules/
libs/
├─ example-library/
│  ├─ example-file.server.ts
...

As it stands, if you attempt to name a file inside the example library with .server or .client, it will have no effect. It would be great if there was an option within AppConfig to allow you to specify directories for this to work in rather than hardcoding just the it to appDirectory.

Is this something that would be accepted as a PR?

[jrestall]

Would also love to see this changed, currently also using a monorepo and having to patch Remix's emptymodulesplugin code to ensure server code in libs is removed from the browser bundle as discussed at remix-run/blues-stack#65 (comment)

I'm sure there is a better way to exclude node_modules from this convention without excluding everything outside the app folder.