Maint: configuration Openvpn selection structure

- Move network protocol from ServerSelection to OpenVPNSelection child
- Move PIA encryption preset from ServerSelection to OpenVPNSelection child
- Move custom port from ServerSelection to OpenVPNSelection child

internal/provider/privado/connection.go

@@ -16,7 +16,7 @@ func (p *Privado) GetOpenVPNConnection(selection configuration.ServerSelection)
 	connection models.OpenVPNConnection, err error) {
 	const port = 1194
 	const protocol = constants.UDP
-	if selection.TCP {
+	if selection.OpenVPN.TCP {
 		return connection, fmt.Errorf("%w: TCP for provider Privado", ErrProtocolUnsupported)
 	}