add systemd replacement for ceph init script

add systemd replacement for ceph init script

the old sys V init script does a lot of stuff, most of which
is already replaced with the system units since jewel,
except for the OSD activation which is still done by either
udev or the old init script.

include systemd service as drop in replacement for the init
script when using jewel. the service is not enabled by
default (as this would break hammer), but needs to be copied
to /etc/systemd/system on upgrade to (manual) or install of
jewel (automatic).

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>