acme: fix service_triggers on config change

acme: fix service_triggers on config change

In the current implementation, the config change trigger is no longer set
at boot time. This is because during boot, only the '$CHALLENGE_DIR' is
created with the boot function. The 'start_service' is first called by first
cron call at midnight. This call is installing the service_triggers reload
handling.

To fix this, add a new extra_command 'renew' that is responsible to renew
the acme. This function is called from cron and the start_service
function does the rest.

* Create directories
* Install service reload trigger form acme config change

Fixes: 76f17ab15b (acme-common: Create challenge directory on boot)
Signed-off-by: Florian Eckert <redacted>