Create `skywire-cli vpn` command

[jdknives]

Feature description

Working with the CLI for the VPN needs to be improved. Currently there are a range of features that we should provide:

• get list of remote vpns with filters (by country for now, by connection metrics would be nice as well)
• connect to VPN server
• get status (returns info about VPN config and connection stats)

Is your feature request related to a problem? Please describe. Using the VPN client on the CLI is not a very pleasant experience.

[0pcom]

PR #1317