Wireguard support for Mullvad and Windscribe (#565)

- `internal/wireguard` client package with unit tests
- Implementation works with kernel space or user space if unavailable
- `WIREGUARD_PRIVATE_KEY`
- `WIREGUARD_ADDRESS`
- `WIREGUARD_PRESHARED_KEY`
- `WIREGUARD_PORT`
- `internal/netlink` package used by `internal/wireguard`

maintenance.md

@@ -11,6 +11,7 @@
 
 - Filter servers by protocol for all
 - Multiple IPs addresses support for all proviedrs
+- Use `internal/netlink` in firewall and routing packages
 
 ## Code