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`

internal/updater/providers/windscribe/sort.go

@@ -10,6 +10,9 @@ func sortServers(servers []models.WindscribeServer) {
 	sort.Slice(servers, func(i, j int) bool {
 		if servers[i].Region == servers[j].Region {
 			if servers[i].City == servers[j].City {
+				if servers[i].Hostname == servers[j].Hostname {
+					return servers[i].VPN < servers[j].VPN
+				}
 				return servers[i].Hostname < servers[j].Hostname
 			}
 			return servers[i].City < servers[j].City