KIP-912 — Support decreasing send's max block time without worrying about metadata's fetch

Discussion Kafka 4.2 Producer

KIP-912 adds two producer configs—`max.block.ms.include.metadata` (boolean, default true) and `max.block.metadata.ms` (default 60s)—to allow separating the metadata-fetch timeout from the record-accumulator block timeout in `KafkaProducer.send()`. When a producer starts cold, the first `send()` blocks for metadata retrieval, and the shared `max.block.ms` budget cannot be reduced below the metadata-fetch duration (often 4+ seconds), preventing operators from setting a shorter blocking limit for record buffering.

Details