KIP-591 — Add Kafka Streams config to set default state store

Accepted Kafka 3.2 Streams

Adds a new Kafka Streams config `default.dsl.store` that lets users globally switch the DSL operator state store type (e.g., `rocksdb` vs `in_memory`) without modifying each operator individually via `Materialized`. Currently, switching all DSL state stores from RocksDB to in-memory (e.g., for Kubernetes deployments without local disks) requires tedious per-operator `Materialized` configurations.

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