Add "subFolder" attribute to "telemetry send" node

[riney92]

It would be helpful if a subfolder can be configured in the "telemetry send" node as described here: https://cloud.google.com/iot/docs/how-tos/mqtt-bridge#publishing_telemetry_events_to_additional_cloud_pubsub_topics (Publishing telemetry events to additional Cloud Pub/Sub Topics).

Thanks a lot!

[kolban-google]

Another user ... created a pull request which seems to add the subFolder ... I believe that may be related to your issue. Many thanks for raising it. I have merged the pull request.