add libvirt and virt manager

modules/optionnals/libvirt.nix

@@ -0,0 +1,21 @@
+{
+  pkgs,
+  username,
+  ...
+}:
+{
+  virtualisation = {
+    libvirtd = {
+      enable = true;
+      qemu = {
+        package = pkgs.qemu_full;
+        runAsRoot = true;
+        swtpm.enable = true;
+      };
+    };
+
+  };
+  users.users.${username} = {
+    extraGroups = [ "libvirtd" ];
+  };
+}