Code review comment for ~ballot/charm-prometheus-alertmanager/+git/charm-prometheus-alertmanager:log-level

I'd like to see this charm go into a blocked state for an incorrectly configured log level value, and would appreciate seeing the values accepted for log-level in the config.yaml description.

I am also concerned that this change when upgrade-charm runs will restart the service (which is typically frowned upon) even if no configuration change is expected. Maybe the default should be a blank string, which equates to not setting a --log.level, which should keep the config file from being updated and the service from restarting based on service context change.