cephadm: KillMode=none in unit file

cephadm: KillMode=none in unit file

The unit already has a ExecStop command that runs 'podman|docker stop',
so systemd should not *also* try to kill the process or else it may
screw up the container state

From https://www.redhat.com/sysadmin/podman-shareable-systemd-services

"Note: It’s important to set the kill mode to none. Otherwise, systemd
will start competing with Podman to stop and kill the container processes.
which can lead to various undesired side effects and invalid states."

Hopefully-fixes: https://tracker.ceph.com/issues/43883
Signed-off-by: Sage Weil <sage@redhat.com>