Kafka source crashes when experiencing backpressure from indexer and waits for too long

[guilload]

"Maximum application poll interval (max.poll.interval.ms) exceeded".

[guilload]

Reported in #2080.

cc @guidao

[guilload]

The Kafka source now does a better job at logging the values (max poll interval and session timeout) that can lead to the consumer crashing when experiencing backpressure.

Downstream, the indexing pipeline has been improved to lead to less backpressure.