Exposes JMX for brokers, to typical monitoring setups

Already included in #49, but here we don't add any export container to the pod.

Can be utilized by kafka-manager (#83) - just tick the JMX box when adding a cluster -
to see bytes in/out rates.

kafka/50kafka.yml

@@ -43,11 +43,15 @@ spec:
         env:
         - name: KAFKA_LOG4J_OPTS
           value: -Dlog4j.configuration=file:/etc/kafka/log4j.properties
+        - name: JMX_PORT
+          value: "5555"
         ports:
         - name: inside
           containerPort: 9092
         - name: outside
           containerPort: 9094
+        - name: jmx
+          containerPort: 5555
         command:
         - ./bin/kafka-server-start.sh
         - /etc/kafka/server.properties