nixbld: automatically build and set up netboot nixos installer

nixbld-etc-nixos/configuration.nix

@@ -422,7 +422,7 @@ in
       dhcp-match = "set:ipxe,175"; # https://forum.ipxe.org/showthread.php?tid=6077
       dhcp-boot = [
         "tag:!ipxe,ipxe.efi"
-        "tag:ipxe,http://perso.m-labs.hk/sb/netboot/netboot.ipxe"
+        "tag:ipxe,http://m-labs.hk/nuc-netboot/netboot.ipxe"
       ];
       enable-tftp = netifLan;
       tftp-root = "${pkgs.ipxe}";
@@ -797,6 +797,7 @@ in
             expires 60d;
           '';
         };
+        locations."/nuc-netboot/".alias = "${import ./defenestrate}/";
 
         # legacy URLs, redirect to avoid breaking people's bookmarks
         locations."/gateware.html".extraConfig = ''