Send response to sensor on successful processing

Integrate downlinks to device to ack the data as successfully inserted into the db and data can be cleared from local non-volatile storage on the sensor.

See https://www.thethingsindustries.com/docs/integrations/webhooks/scheduling-downlinks/ for how to do. Will need to store some secrets relating to the API and application ids.

The issue names no files, tests, or entry points. Start by locating the successful database-insertion path, then consult the Things Industries scheduling-downlinks documentation and determine how API secrets and application IDs are stored. Done means a successful insertion triggers a sensor acknowledgement and allows local non-volatile data to be cleared.

Written by the indexing model from the issue text.