Make the .server and .client folder names configurable

[heivo]

I like the possibility to move all server-only or client-only modules inside a dedicated folder, however the leading dot in the default folder names (.server and .client) has some drawbacks:

• those folders are hidden by default in Linux
• the tsconfig.json include config has to be adjusted (e.g. { "include": ["app/.server/**/*.ts"] })
• eslint has to be configured to not exclude files within those folders (e.g. { "ignorePatterns": ['!app/.server/'] })

It would be nice if the name of those folders were configurable, for example:

export default defineConfig({
  plugins: [
    remix({
      serverModulesDirectory: 'server',
      clientModulesDirectory: 'client',
    }),
  ],
})