Update the DeviceConfigRestService with API to download the actual backup configuration data (binary or text) for a single or multiple device configurations.

Suggested API URL:

GET /rest/device-config/download/{id} with 'device_config' table id, gets latest backup (if any) for that specific entry

POST /rest/device-config/download with a Json payload in form "{ ids: [] }" or similar with 'device_config' table IDs to download, response will be a zip file with one entry for each id, possibly with additional human-readable naming scheme.