title: Identify group leader in librdkafka
body: <p>Is there a way to identify the group leader in librdkafka ?</p>
  
  <p>As there is no way to pass a custom partition strategy, I am having some hack to serve the purpose. My specific consumer has to be the group leader if not I should exit.</p>
  
  <p>Or is there a way to make sure there is no other consumer running with the current consumer group id ?</p>