More temporary builders

While the long-term plan is to start collecting funds for a dedicated CI through the NixOS OpenCollective (https://github.com/SomeoneSerge/nixpkgs-cuda-ci/issues/11), for the time being we need more builders for https://hercules-ci.com/github/SomeoneSerge/nixpkgs-cuda-ci. @ConnorBaker is willing to provide some extra compute. We're going to need separate cachix keys for his machines (note that cachix keys used by the builders can be freely rotated), CC @samuela / please check the nixos cuda matrix room