KIP-718 — Make KTable Join on Foreign key unopinionated

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Fixes `KTable` foreign key join to respect the `Materialized` store type passed by the user for the internal subscription store, instead of always using RocksDB. The KIP-213 implementation hardcodes RocksDB for the internal subscription store regardless of the `Materialized` configuration, causing test failures on Windows (RocksDB file locking) and violating the contract of in-memory materialization.

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