Running zilla with the `kafka-grpc` binding in a cluster with multiple instances results in each instance delivering a message to the configured `remote_server`

[vordimous]

Describe the bug
Running 3 zilla instances with the exact same config delivering messages to a gRPC service using the kafka-grpc binding results in each zilla instance delivering the same message.

To Reproduce
Steps to reproduce the behavior:

1. run the grpc.kafka.proxy example with replica count of 3
2. 3 messages are delivered to the gRPC service

Expected behavior
Zilla should respect the consumer group rules and distribute messages across zilla instances. (n) number of zilla instances should work with (n) number of partitions for the same topic.