feat(tdx): add nix build for TDX google VMs

Signed-off-by: Harald Hoyer <harald@matterlabs.dev>

lib/default.nix

@@ -0,0 +1,3 @@
+{ ... }: {
+  nixosGenerate = import ./nixos-generate.nix;
+}

lib/nixos-generate.nix

@@ -0,0 +1,33 @@
+{ pkgs
+, nixosSystem
+, formatModule
+, system
+, specialArgs ? { }
+, modules ? [ ]
+}:
+let
+  image = nixosSystem {
+    inherit pkgs specialArgs;
+    modules =
+      [
+        formatModule
+        (
+          { lib, ... }: {
+            options = {
+              fileExtension = lib.mkOption {
+                type = lib.types.str;
+                description = "Declare the path of the wanted file in the output directory";
+                default = "";
+              };
+              formatAttr = lib.mkOption {
+                type = lib.types.str;
+                description = "Declare the default attribute to build";
+              };
+            };
+          }
+        )
+      ]
+      ++ modules;
+  };
+in
+image.config.system.build.${image.config.formatAttr}