Harvest public Thingspeak api

[nuest]

Documentation: https://thingspeak.com/docs/channels#index

Example: https://api.thingspeak.com/channels/public.json

Current harvester: https://github.com/52North/OpenSensorSearch/blob/c07f02d7a51f9d78d1b82cf51236befca64e8514/service/src/test/resources/Requests/harvestThingSpeak.js#