Add support for Kafka record headers (#1025)

Added support for Kafka headers to be passed and retrieved from functions. The headers and supported and work only for Kafka version 0.11.0.0 and higher.

test/tests/mqtrigger/kafka/kafka_pub/kafka-pub.go

@@ -14,14 +14,18 @@ func Handler(w http.ResponseWriter, r *http.Request) {
 	producerConfig.Producer.RequiredAcks = sarama.WaitForAll
 	producerConfig.Producer.Retry.Max = 10
 	producerConfig.Producer.Return.Successes = true
+	producerConfig.Version = sarama.V0_11_0_0
 	producer, err := sarama.NewSyncProducer(brokers, producerConfig)
 	fmt.Println("Created a new producer ", producer)
 	if err != nil {
 		panic(err)
 	}
+
+	headers := []sarama.RecordHeader{{Key: []byte("Z-Custom-Name"), Value: []byte("Kafka-Header-test")}}
 	_, _, err = producer.SendMessage(&sarama.ProducerMessage{
-		Topic: "testtopic",
-		Value: sarama.StringEncoder("{\"name\": \"testvalue\"}"),
+		Topic:   "testtopic",
+		Value:   sarama.StringEncoder("{\"name\": \"testvalue\"}"),
+		Headers: headers,
 	})
 
 	if err != nil {