Support Multi Event Stream in SR

[arunvasudevan]

Desired Behavior

As per Martin Kleepman's article (https://www.confluent.io/blog/put-several-event-types-kafka-topic/), support multi events with different schema types within a stream.

Benefits

Consumers could use the same stream to publish multiple events.

• Reduces the no.of streams created.
• Group similar/transformed events in one stream.