Generate separate Nix modules in a directory

[aksiksi]

This behavior would be controlled by a flag with default = false.

Directory structure:

$ ls
service-a.nix
service-b.nix
volumes.nix
networks.nix
default.nix

Where default.nix looks something like this:

{ ... }:

{
  imports = [
    ./service-a.nix
    ./service-b.nix
    ./volumes.nix
    ./networks.nix
  ];

  # Preamble.
  
  # Root target.
}