Create template variables for a device for the first time.

Example:

Existing variables:
None

Variables provided in this request body:
{"_sys_serial": "AB0011111", "_sys_lan_mac": "11:12:AA:13:14:BB", "SSID_A": "Z-Employee"}

Final output variables:
{"_sys_serial": "AB0011111", "_sys_lan_mac": "11:12:AA:13:14:BB", "SSID_A": "Z-Employee"}