KIP-759 — Unneeded repartition canceling

Accepted Streams

Adds a `repartitionRequired` flag to Kafka Streams' internal graph optimization so that a `selectKey`/`map` followed by a `groupByKey` does not insert an unnecessary repartition topic when the upstream stream is already partitioned by the new key. Every key-changing operation currently forces a repartition before any stateful aggregation, even when the resulting key is identical to the existing partition key, wasting network bandwidth and adding end-to-end latency.

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