[Feature] Include networkmanager-openvpn in base image

[brendenhoffman]

There is no reason a vpn should not be able to be configured on the steam deck, while there is little use for one outside of desktop mode, the lack of the packages which many vpns use makes it very hard to configure one if we choose to do so. The openvpn package is essential, however including networkmanager-openvpn would integrate seamlessly in KDE. Current SteamOS 3.3 beta