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/hellokafka.js

@@ -1,9 +1,13 @@
 
 module.exports = async function (context) {
     console.log(context.request.body);
+    console.log("z-custom-name: " + context.request.headers['z-custom-name']);
+    console.log("x-fission-function-name: " + context.request.headers['x-fission-function-name']);
     let obj = context.request.body;
+    let headers = context.request.headers;
     return {
         status: 200,
+	headers: headers,
         body: obj
     };
 }