fedora-common-ostree: Add systemd-container

This pakage provides `machinectl` and `systemd-nspawn`, which is useful
as a container tools itself or as a better alternative to sudo to run
commands under another user in a clean shell session.

See: https://github.com/fedora-silverblue/issue-tracker/issues/503

fedora-common-ostree.yaml

@@ -36,6 +36,8 @@ packages:
   - buildah
   - podman
   - skopeo
+  # See: https://github.com/fedora-silverblue/issue-tracker/issues/503
+  - systemd-container
   # Provides terminal tools like clear, reset, tput, and tset
   - ncurses
   # Flatpak support