custom cfg
https://logging.apache.org/log4j/2.0/manual/customconfig.html
https://logging.apache.org/log4j/2.0/manual/extending.html#ConfigurationFactory

custom cfg factory
    https://github.com/eugenp/tutorials/tree/master/logging-modules/log4j2
    -Dlog4j2.configurationFactory=com.baeldung.log4j2.CustomConfigFactory
    @Plugin(name = "CustomConfigurationFactory", category = ConfigurationFactory.CATEGORY)
    @Order(50)
    public class CustomConfigFactory extends ConfigurationFactory {
        // ... rest of implementation
    }

custom log levels
https://logging.apache.org/log4j/2.x/manual/customloglevels.html