Create template variables for all devices for the first time.

Example:

Existing variables:
None

Variables provided in this request body:
{"AB0011111": {"_sys_serial": "AB0011111", "_sys_lan_mac": "11:12:AA:13:14:BB", "SSID_A": "Z-Employee"},
"AB0022222": {"_sys_serial": "AB0022222", "_sys_lan_mac": "21:22:AA:23:24:BB", "vc_name": "Instant-23:24:BB"}}

Final output variables:
{"AB0011111": {"_sys_serial": "AB0011111", "_sys_lan_mac": "11:12:AA:13:14:BB", "SSID_A": "Z-Employee"},
"AB0022222": {"_sys_serial": "AB0022222", "_sys_lan_mac": "21:22:AA:23:24:BB", "vc_name": "Instant-23:24:BB"}}