Update values of existing template variables and add new variabels to the existing set of variables for a device.

Example:

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

Variables provided in this request body:
{"SSID_A": "X-Employee", "vc_name": "Instant-13:14:BB"}

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

In Final output variables "SSID_A" is updated and "vc_name" is created.