KIP-375 — Kafka Clients - make Metadata#TOPIC_EXPIRY_MS configurable

Discussion Client

Makes `Metadata.TOPIC_EXPIRY_MS` (the TTL for unused topic metadata in the client cache) configurable via a new `metadata.max.idle.ms` producer/consumer config. In high-throughput, low-latency systems, periodic metadata refresh triggered by topic expiry adds unexpected latency spikes to the caller thread.

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