nixos/wg-access-server: bugfix missing cfg dns.enabled (#352839)

nixos/modules/services/networking/wg-access-server.nix

···
       type = lib.types.submodule {
         freeformType = settingsFormat.type;
         options = {
-          dns.enable = mkOption {
+          dns.enabled = mkOption {
             type = types.bool;
             default = true;
             description = ''