Slf4JLoggingSystem should also configure JUL levels

[farrault]

As discussed here, by default SLF4JBridgeHandler only receives INFO or higher JUL logs

And so, enabled lower levels in application.properties with "logging.level.xxx" properties doesn't allow to see JUL logs lower than INFO

"logging.level.xxx" properties should also be applied to JUL loggers (in addition to Sl4jf loggers) in order to SLF4JBridgeHandler to receive all the enabled logs

[trecloux]

If you are using logback, JUL should now also be configured : #3926