Currently, the Dockerfile expects /etc/systemd/journald.conf to exist on the base container,
but sometimes this may not be the case, for example on Fedora 40, which causes
the build process to fail if the host machine is also running Fedora 40.
Update the dockerfile to create a conf.d file instead, which has higher precedence.
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1972