Kafka test with specialized serializer and deserializer

`KafkaConsumerHelper#convertProtobufToJson` and `KafkaProducerHelper#buildProtoMessage` assume that we're using `ByteArrayDeserializer` and `ByteArraySerializer`. They expect the `ConsumerRecord#value()` to be a `byte[]` or return a `byte[]`. This is problematic when using special SerDes that handle the low level parsing/serialization; for example, the SerDes from https://github.com/awslabs/aws-glue-schema-registry or Confluent's SerDes for their Schema Registry. These libraries handle the POJOs directly, i.e. `ConsumerRecord#value()` will be of type `MessageOrBuilder`, and no further parsing (via Reflection) will be needed. There should be a property that allows overriding the default behavior so `KafkaConsumerHelper` and `KafkaProducerHelper` just accept/return POJO of the wire type instead of `byte[]`.