feature: add command to test the vpn with system privileges

[ainghazal]

Checklist

• I have read the contribution guidelines
• Iff you changed code related to services, or inter-service communication, make sure you update the diagrams in ARCHITECTURE.md.
• Reference issue for this pull request: refactor to use a layered architecture #47

Description

This is a transient command to be able to test the VPN given administrator privileges. It will create a tun interface, setup routes, and move all system traffic over the tun. Useful for testing the current architecture and do performance tests against OpenVPN.

We still need to converge the current legacy binary app, that could take different commands to behave as ping , a socks5 proxy, or just fetch a remote resource over the VPN using gvisor, but we will do that at a later point.

[bassosimone]

Unclear to me whether we want to merge this or just update the minivpn binary.

[ainghazal]

good question - we should discuss. at this point, I think we can just replace the binary after merging other outstanding PRs. I will update this branch with the latest modifications. the good thing is that the integration test does not depend on the binary interface.

[ainghazal]

closing in favor of #66