...

• extend to() / addSink() with a "broadcast" option/config in KafkaStreams.
• add toAllPartitions() / addBroadcastSink() methods in KafkaStreams.
• allow StreamPartitioner to return `-1` for "all partitions".
• Adding a separate class to handle multi casting. This was rejected in favour of enhancing the current StreamPartitioner  interface.

Test Plan

• Add new tests(unit/integration) similar to the partition  tests for the newly introduced partitions  method.
• Add tests to fail when a non singleton set is returned for FK joins/IQ cases.