title: Consuming from multiple topics using single kafka stream
body: <p>which one is recommended to use : 
  1. Single kafka stream consuming from multiple topics
  2. Different kafka streams consuming from different topics (I've used this one already with no issues encountered)</p>
  
  <p>Is it possible to achieve #1 ? and if yes, what're the implications?
  and if I use 'EXACTLY_ONCE' settings, what kind of complexities it'll bring?</p>
  
  <p>kafka version : 2.2.0-cp2</p>