adds the logger_name and thread_name labels for logback

[jeantil]

This is a proposal to add logger_name and thread_name as first-class labels in logback appender which fixes #107

A possible alternative with less impact but more hackish could be to include these values as members of the mdc properties ,for example:

    @Override
    protected void append(ILoggingEvent event) {
        String logLevel = event.getLevel().toString();
        ByteBuffer logLine = actualEncoder.apply(event);
        Map<String, String> mdcPropertyMap = event.getMDCPropertyMap();
        
        mdcPropertyMap.put("logback_logger_name", event.getLoggerName());
        mdcPropertyMap.put("logback_thread_name", event.getThreadName());
        
        LabelSerializer labelSerializer = LabelSerializers.threadLocal();
        appendLogLabel(labelSerializer, logLevel);
        appendMdcLogLabels(labelSerializer, mdcPropertyMap);

        logger.log(
                event.getTimeStamp(),
                0L,
                labelSerializer,
                logLine
        );
    }