Motivation for this change

Personally, I have a pulseaudio setup where I have all my clients connect to a remote server.
This can be easily achieved by setting the PULSE_SERVER environmental variable.

I would say this is a general enough approach to solve my problem, that it might be useful for other users and other purposes, like settings environmental variables to tell your GPU driver to do something non-default.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option 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.