[VOL-1505]  This update enables the core to add a key when
publishing an event onto kafka.   The corresponding update is
done in the adapter GO components.   Similar changes remain to
be done in pyvoltha.

Change-Id: I0bb1e3cb8c2fa9e0214f96d863819755d34a0bb9
diff --git a/protos/inter_container.proto b/protos/inter_container.proto
index ac2af4f..4d4ffe8 100644
--- a/protos/inter_container.proto
+++ b/protos/inter_container.proto
@@ -48,7 +48,8 @@
     MessageType type = 2;
     string from_topic = 3;
     string to_topic = 4;
-    int64 timestamp = 5;
+    string key_topic = 5;
+    int64 timestamp = 6;
 }
 
 message Argument {