custom metadata populated by grpc-server missing

[ankitk-me]

Describe the bug
Custom metadata populated by grpc-server was missing while trying to consume messages.

To Reproduce
grpc.kafka.proxy

Steps to reproduce the behavior:

• update the grpc-service to include custom metadata as part of response.

   ctx.set('foo', 'bar')
  

• start example

  ./startup.sh
  

• call EchoUnary rpc on grpc EchoService service.

• Incoming response is missing custom metadata.

Expected behavior
grpc custom metadata should pass through.