Add support for OpenVPN

[TheRedSpy15]

Currently, openvpn servers ignore the set proxy

[himanshub16]

I'm not very used to using openvpn from CLI. I mostly get VPN configs (from vpngate) and import that in GNOME network settings. The GUI has an option to provide proxy settings.

I cannot figure out an elegant way to do this.
One way could be modifying vpn.data, and vpn.secrets attribute using nmcli con modify for every VPN connection.
Or doing the same for VPN settings in /etc/NetworkManager/system-connections/.

However, I don't find them good solutions as they need to run after every new connection is created, and sounds ugly.
Thoughts?

[tatarins]

I also have problems with openvpn and Proxyman! Internet is missing! Reconnecting helps!

[tatarins]

When fix?

[tatarins]

?

[himanshub16]

Sorry @tatarins!
I don't have much bandwidth these days to work on more features.
Also, IMHO VPN is not a very sought after functionality on Linux.

If someone would volunteer for a PR, I'll be happy to review and merge it.
Thanks :)