Issue description

I've collected multiple issues regarding virt-manager not being able to save its settings due to programs.dconf.enable = true; wasn't set. (Sorted from most recent to least, #255837 #67736 #52777 #42433 #11844 #2448)

This problem has been happening since 2014, spanning almost ten years.

To my knowledge, because Gnome requires dconf, this option isn't needed to be set on Gnome. Several people suggested to have dconf as a dependency to virt-manager, but as a response from #42433 (comment) mentioned -

gnome3.dconf is a system service that needs to be added to services.dbus.packages by your desktop environment. If you create your own environment, you will need to add it yourself (adding programs.dconf.enable = true; to configuration.nix should work). Nix does not contain a mechanism for representing a dependency on a service.

Under almost every issue mentioned ideas to improve UX (except #11844 which was marked as a duplicate of #2448), but as far as I know, there's no progress.

Also, to the best of my knowledge, there's also no mention of this problem in the NixOS manual. The line is included in wiki.nixos.org, but with no explanation as to why.

Some ideas to explore

• Have programs.dconf.enable = true; inside virt-manager by making a programs.virt-manager.enable option
  • virt-manager cannot save settings anymore #2448 (comment), virt-manager doesn't save config #67736 (comment)
• Include some sort of warning when building the nixos configuration when dconf is not detected on system
  • virt-manager needs dconf as runtime dependencie to store settings #52777 (comment)
• Add documentation in the NixOS manual to set programs.dconf.enable = true;

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