feat: topic event request add metadata field (#319)

Author: Lei, Hwang

sdk/java-sdk/sdk/src/main/java/io/mosn/layotto/v1/grpc/PubsubConverter.java

@@ -98,6 +98,7 @@ public static TopicEventRequest TopicEventRequest2Domain(AppCallbackProto.TopicE
         result.setType(req.getType());
         result.setSpecVersion(req.getSpecVersion());
         result.setContentType(req.getDataContentType());
+        result.setMetadata(req.getMetadataMap());
         ByteString byteString = req.getData();
         if (byteString == null) {
             result.setData(new byte[]{});