Move the inline modularServicesModule to a separate file so the module
system sets _file automatically from the file path, removing the need
for __curPos.
Render documentation for modular services.
https://nixos.org/manual/nixos/unstable/#modular-services
This is admittedly not a great solution, but it is a rather simple
solution that we can use until we develop a proper one.
Flaws:
- These are rendered in the NixOS documentation, but modular services
are not meant to be exclusive to NixOS.
- They are rendered as NixOS options, but should be imported into
service submodules.
Benefits:
- Simple
- search.nixos.org integration for free
