default SystemProducer getProducer(String systemName, Config config, MetricsRegistry registry, String producerLabel) {
    return getProducer(systemName, config, registry);
  }
This function provides an extra input parameter to {@link #getProducer}, which can be used to provide extra
information for the producer instance, e.g. ownership of client instance, to help better identify producers in logs,
threads and client instances etc., along with other relevant information like systemName.

@param systemName The name of the system to create producer for.
@param config The config to create producer with.
@param registry MetricsRegistry to which to publish producer specific metrics.
@param producerLabel a string to provide info the producer instance.
@return A SystemProducer
samza-api/src/main/java/org/apache/samza/system/SystemFactory.java