mgr/cephadm: Allow customizing mgr/cephadm/lsmcli_blink_lights_cmd per host

mgr/cephadm: Allow customizing mgr/cephadm/lsmcli_blink_lights_cmd per host

* Rename key name from 'lsmcli_blink_lights_cmd' to 'blink_device_light_cmd'
* Refactor TemplateMgr::render() method to use the Ceph common behavior how to name store/module option keys. The old implementation required a key like 'mgr/cephadm/services_nfs_ganesha.conf' instead of 'mgr/cephadm/services/nfs/ganesha.conf' or 'mgr/cephadm/mgr0_blink_device_light_cmd' instead of 'mgr/cephadm/mgr0/blink_device_light_cmd'.

Fixes: https://tracker.ceph.com/issues/48041
Signed-off-by: Volker Theile <vtheile@suse.com>