Motivation for this change

BURP is currently available in nixpkgs but provides no services

Things done

• 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.

The client service has been tested locally with success.
The server service has not been tested yet.

Aspects pending a better solution:

• burp client rewrites the config file (burp.conf) with information obtained from the server on first connection. This is true even if no change is introduced. Reported upstream: Configuration file is rewritten even when no change is introduced grke/burp#620
• a workaround is in place that copies burp.conf from /nix/store to /var/lib/burp.

PS: This is my first attempt at writing a nixos module so any additional feedback is welcome.