Motivation for this change

Some packages install their dbus config files to share/dbus-1/system.d instead
of etc/dbus-1/system.d, so look in both places.

Specifically this happens with colord, which breaks the Night Light feature on Gnome Shell. A nix-locate search makes it clear that this location is uncommon, with usbguard being the only other package that uses it.

However it seems like this is a standard location according to the dbus manual (my emphasis):

This is intended to allow extension of the system bus by particular packages. For example, if CUPS wants to be able to send out notification of printer queue changes, it could install a file to /usr/share/dbus-1/system.d or /etc/dbus-1/system.d that allowed all apps to receive this message and allowed the printer daemon user to send it.

So instead of patching specific packages, looking for .conf files in share/dbus-1/system.d by default seems sane.

Things done

Running my system with the commit makes Night Light work

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.