Add VPN metrics
Look like this:
# HELP vpn_server_connections_list VPN server connections list
# TYPE vpn_server_connections_list gauge
vpn_server_connections_list{local_ip="192.168.27.65",name="rx_bytes",src_ip="85.72.161.23",user="saphoooo",vpn="ipsec"} 39290
vpn_server_connections_list{local_ip="192.168.27.65",name="tx_bytes",src_ip="85.72.161.23",user="saphoooo",vpn="ipsec"} 44530