KIP-955 — Add stream-table join on foreign key

Discarded Streams

Adds a foreign-key stream-table join operator to Kafka Streams that joins a `KStream` to a `KTable` on a non-primary key extracted from the stream record's value. Without this, normalized data models with foreign key relationships require manual re-keying, multiple repartition topics, and complex multi-step topologies to replicate basic SQL FK joins.

Details