Make syncthing optional

flake.nix

@@ -76,6 +76,7 @@
                   username = "abby";
                   inherit inputs;
                   system = system;
+                  use_syncthing = true;
                 };
               }
             ];
@@ -99,6 +100,7 @@
               inherit system;
               username = "abby";
               inherit inputs;
+              use_syncthing = false;
             };
           };
       homeConfigurations."pager@nicrosil" =
@@ -122,6 +124,7 @@
               inherit system;
               username = "pager";
               inherit inputs;
+              use_syncthing = false;
             };
           };
     };