vars: introduce share flag

nixosModules/clanCore/vars/default.nix

@@ -39,7 +39,12 @@ in
     vars = {
       generators = lib.flip lib.mapAttrs config.clan.core.vars.generators (
         _name: generator: {
-          inherit (generator) dependencies finalScript prompts;
+          inherit (generator)
+            dependencies
+            finalScript
+            prompts
+            share
+            ;
           files = lib.flip lib.mapAttrs generator.files (_name: file: { inherit (file) secret; });
         }
       );

nixosModules/clanCore/vars/interface.nix

@@ -168,6 +168,15 @@ in
               internal = true;
               visible = false;
             };
+            share = {
+              description = ''
+                Whether the generated vars should be shared between machines.
+                Shared vars are only generated once, when the first machine using it is deployed.
+                Subsequent machines will re-use the already generated values.
+              '';
+              type = bool;
+              default = false;
+            };
           };
         })
       );