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/purevpn/connection.go

@@ -11,7 +11,7 @@ func (p *Purevpn) GetOpenVPNConnection(selection configuration.ServerSelection)
 	connection models.OpenVPNConnection, err error) {
 	protocol := constants.UDP
 	var port uint16 = 53
-	if selection.TCP {
+	if selection.OpenVPN.TCP {
 		protocol = constants.TCP
 		port = 80
 	}

internal/provider/purevpn/filter.go

@@ -15,8 +15,8 @@ func (p *Purevpn) filterServers(selection configuration.ServerSelection) (
 			utils.FilterByPossibilities(server.Country, selection.Countries),
 			utils.FilterByPossibilities(server.City, selection.Cities),
 			utils.FilterByPossibilities(server.Hostname, selection.Hostnames),
-			selection.TCP && !server.TCP,
-			!selection.TCP && !server.UDP:
+			selection.OpenVPN.TCP && !server.TCP,
+			!selection.OpenVPN.TCP && !server.UDP:
 		default:
 			servers = append(servers, server)
 		}