Maint: make VPN connection not specific to OpenVPN

- Add VPN field to ServerSelection struct
- Set VPN type to server selection at start using VPN_TYPE
- Change OpenVPNConnection to Connection with Type field
- Rename Provider GetOpenVPNConnection to GetConnection
- Rename GetTargetIPOpenVPNConnection to GetTargetIPConnection
- Rename PickRandomOpenVPNConnection to PickRandomConnection
- Add 'OpenVPN' prefix to OpenVPN specific methods on connection

internal/provider/surfshark/connection.go

@@ -7,8 +7,8 @@ import (
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
-func (s *Surfshark) GetOpenVPNConnection(selection configuration.ServerSelection) (
-	connection models.OpenVPNConnection, err error) {
+func (s *Surfshark) GetConnection(selection configuration.ServerSelection) (
+	connection models.Connection, err error) {
 	protocol := constants.UDP
 	var port uint16 = 1194
 	if selection.OpenVPN.TCP {
@@ -21,10 +21,11 @@ func (s *Surfshark) GetOpenVPNConnection(selection configuration.ServerSelection
 		return connection, err
 	}
 
-	var connections []models.OpenVPNConnection
+	var connections []models.Connection
 	for _, server := range servers {
 		for _, IP := range server.IPs {
-			connection := models.OpenVPNConnection{
+			connection := models.Connection{
+				Type:     selection.VPN,
 				IP:       IP,
 				Port:     port,
 				Protocol: protocol,
@@ -34,8 +35,8 @@ func (s *Surfshark) GetOpenVPNConnection(selection configuration.ServerSelection
 	}
 
 	if selection.TargetIP != nil {
-		return utils.GetTargetIPOpenVPNConnection(connections, selection.TargetIP)
+		return utils.GetTargetIPConnection(connections, selection.TargetIP)
 	}
 
-	return utils.PickRandomOpenVPNConnection(connections, s.randSource), nil
+	return utils.PickRandomConnection(connections, s.randSource), nil
 }