Removing Kafka Cache Bindings Causes `grpcurl` to Fail with Missing Content-Type Error

[ankitk-me]

Describe the bug
When attempting to echo a message using the grpcurl client with the grpc-kafka configuration in Zilla, excluding the kafka cache bindings results in an error [malformed header: missing HTTP content-type].

To Reproduce
Steps to reproduce the behavior:

1. Use zilla-example -> grpc.kafka.echo
2. Remove cache_client & cache_server from the flow.
3. Route grpc-kafka exit to kafka_client.
4. Start the stack using ./setup
5. Trigger grpcurl command

grpcurl -insecure -proto proto/echo.proto  -d '{"message":"Hello World"}' localhost:7153 grpc.examples.echo.Echo.UnaryEcho

6. Observe mentioned error

ERROR:
  Code: Unknown
  Message: malformed header: missing HTTP content-type

Expected behavior
Mentioned output for grpcurl command:

{
  "message": "Hello World"
}