Enhance documentation for logging configuration

[tfr42]

Explaination is required for https://github.com/deegree/deegree3/blob/master/deegree-services/deegree-webservices/src/main/resources/log4j2.properties#L44

rootLogger.level = ${log4j.level}
rootLogger.appenderRefs = stdout
rootLogger.appenderRef.stdout.ref = STDOUT

"Every configuration must have a root logger. If one is not configured the default root LoggerConfig, which has a level of ERROR and has a Console appender attached, will be used. The main differences between the root logger and other loggers are

• The root logger does not have a name attribute.
• The root logger does not support the additivity attribute since it has no parent."

https://logging.apache.org/log4j/2.x/manual/configuration.html

[tfr42]

Add logger names and configuration examples for log4j2 to documentation as in https://github.com/deegree/deegree3/blob/deegree-3.4.20/deegree-services/deegree-webservices/src/main/resources/log4j.properties