install virt-manager

a bit contentious since we don't actually want this to show up to
end users, given vbox can't be used we may need to have some virt
solution for developers though

mkosi.conf.d/99-packages-development.conf

@@ -11,3 +11,4 @@ Packages=cmake
          clazy
          ccache
          flatpak-builder
+         virt-manager