KIP-1304 — Add consumer metric about paused partitions

Discussion ConsumerMetrics

Adds consumer metrics under consumer-coordinator-metrics tracking the number of currently paused partitions, which partitions are paused, how long they have been paused, and the rate of pause calls. The consumer exposes pause()/resume() for flow control and Kafka Streams uses it heavily for backpressure, post-rebalance task initialization, and changelog restore, yet no metric reveals pause state, so stuck consumers and buffer backpressure are invisible to monitoring.

Details