Show “Connected” only after verifying the WireGuard tunnel is alive

[kchudy]

As a user, when I connect to VPN, I want the app to show Connected only when the VPN is actually usable.

Current implementation shows an error after a few minutes when we detect that the tunnel is inactive. That's too late.

AC:

• Update the client apps to display the Connected status only after we confirm the WireGuard tunnel is actually up and passing traffic.
• Add an intermediate Verifying… state between Connect and Connected

[kchudy]

Conclusions after initial refinement:

• Requires monitoring of the handshake process (key exchange) in order to determine the connection status.
• The handshake process monitoring will be different on each OS: kernel on Linux, boringtun on macOS, DLL on Windows.