foris-controller-openvpn_client-module: Add wip vpn-client firewall integration

Add as a patch firewall integration of VPN client. It is currently being discussed in the following merge request:

turris/foris-controller/foris-controller-openvpn_client-module!7 (merged)

This is just a temporally patch to include it before we get all the code style polishing done and new version will be released. Afterwards patch will be dropped.