container/systemd: ensure /var/log/ceph exists

container/systemd: ensure /var/log/ceph exists

This adds a `ExecStartPre=-/usr/bin/mkdir -p /var/log/ceph` in all
systemd service templates for all ceph daemon.
This is specific to RHCS after a Leapp upgrade is done. Indeed, the
`/var/log/ceph` seems to be removed after the upgrade.
In order to work around this issue let's ensure the directory is present
before trying to start the containers with podman.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1949489
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>