KIP-401 — TransformerSupplier/ProcessorSupplier StateStore connecting

Accepted Kafka 2.6 Streams

Allows `ProcessorSupplier` and `TransformerSupplier` implementations to declare their associated state stores via a `stores()` method so callers do not need to separately pass store names when building topologies with `KStream.process()`. The requirement to pass state store names externally alongside the supplier was boilerplate that forced topology builders to know implementation details of the processor.

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