Revert "Revert "switch to org.apache.kafka.clients.producer.KafkaProducer to see if we can avoid the InterruptedException at the end of the crawl (and log warnings on failure to send message)""

This reverts commit a0f70d0865198908e2fa700772ca0694ee079a96.
make sure the kafka producer thread is not in the ToePool thread group, to stop it from being interrupted at the end of the crawl