feat(nix/darwin): HeliPort

Currently disabled because undmg doesn't handle EULAs

REF: https://github.com/matthewbauer/undmg/issues/2

.config/nix/systems/darwin/default.nix

@@ -25,6 +25,7 @@ in
               inherit system brew-api;
               nixpkgs = nixpkgs-stable;
             })
+            (import ../../overlays/darwin/heliport.nix)
           ];
         }
       ) pkgs pkgs-unstable;