SysLog config property replaced with config.factory service closure

The Drupal\syslog\Logger\SysLog class now uses a service closure to lazily load the config.factory service. This works around certain cases of circular references that appear if a config storage dependency (such as an alternative cache backend) requires logging, and a logger depends on config storage. Subclasses should retrieve the configuration from ($this->configFactory)()->get('syslog.settings') rather than $this->config.