KIP-747 — Add support for basic aggregation APIs

Discussion Streams

Adds built-in `min`, `max`, and `sum` aggregation functions to `KGroupedStream`, `KGroupedTable`, `TimeWindowedKStream`, and `SessionWindowedKStream` in Kafka Streams. Developers currently must implement these common aggregations manually in every application, leading to duplicated, potentially suboptimal code scattered across codebases.

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