cephadm: Support Docker Live Restore

cephadm: Support Docker Live Restore

Currently with Docker Live Restore [1] enabled and while restarting
Docker Engine - all Ceph container images will get restarted,
while the feature allows restarting docker.service without
containers downtime.

This is due to Requires=docker.service in systemd units templates,
which mandates that on docker.service restart - the ceph container
systemd units will be restarted as well.

Reworking Requires= to Wants= that is a weaker version of the former,
see [2].

Leaving After= entries, because they should allow systemd to correctly
order the startup (first docker, then ceph containers).

[1]: https://docs.docker.com/engine/daemon/live-restore/
[2]: https://www.freedesktop.org/software/systemd/man/latest/systemd.unit.html#Wants=

Fixes: https://tracker.ceph.com/issues/68028
Signed-off-by: Michal Nasiadka <mnasiadka@gmail.com>