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This lets the users to implement the partitioner with ability to choose partition based on header values.

Make the call to partition method in KafkaProducer to use the new method. Since it is defaulted to use the existing method, this should not cause any behaviour change.

Mark headers as readonly before the first call for

1. Make sure the client cannot update the headers.
2. Ensure consistency as it get marked before the second call.

Total changes : https://github.com/apache/kafka/pull/13981

Compatibility, Deprecation, and Migration Plan

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