Webhooks - Deprecating subscribing to single devices

We deprecated support for subscribing to single devices. In the future, only subscribing to locations will be supported.

For example, it is recommended to not provide devices in EXT-API endpoint POST ext-api.airthings.com/v1/webhooks:

{
  "name": "webhook with locations only",
  "url": "https://webhooks.airthings.com/samples",
  "locations": ["...", "..."]
  // Deprecated: "devices": []
}