systemd domainname unit - use nix store path of net tools for domainname

[josephst]

Description of changes

Recent change to how domainname is set (going from activationScript to systemd unit) causes an error when trying to activate the systemd unit file - getting domainname.service: Failed at step EXEC spawning domainname: No such file or directory.

Fixed by adding full path to nettools to the command (ie serviceConfig.ExecStart = ''${pkgs.nettools}/bin/domainname "${cfg.domain}"'';). Suspect this may be an issue in some other places where activationScripts (which seem to inherit the system's installed packages) have been replaced with systemd unit files (which are isolated and do not inherit from $PATH or installed packages)

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[nikstur]

Thank you!