chore(validation): move functions from constants

- Move validation functions from `internal/constants` to `internal/configuration/settings/validation`
- Concatenate all OpenVPN constants in `internal/constants/openvpn.go`

internal/provider/privateinternetaccess/httpclient.go

@@ -18,7 +18,7 @@ var (
 )
 
 func newHTTPClient(serverName string) (client *http.Client, err error) {
-	certificateBytes, err := base64.StdEncoding.DecodeString(constants.PIACertificateStrong)
+	certificateBytes, err := base64.StdEncoding.DecodeString(constants.PiaCAStrong)
 	if err != nil {
 		return nil, fmt.Errorf("%w: %s", ErrParseCertificate, err)
 	}

internal/provider/privateinternetaccess/openvpnconf.go

@@ -17,17 +17,17 @@ func (p *PIA) BuildConf(connection models.Connection,
 		defaultCipher = constants.AES128cbc
 		defaultAuth = constants.SHA1
 		X509CRL = constants.PiaX509CRLNormal
-		certificate = constants.PIACertificateNormal
+		certificate = constants.PiaCANormal
 	case constants.PIAEncryptionPresetNone:
 		defaultCipher = "none"
 		defaultAuth = "none"
 		X509CRL = constants.PiaX509CRLNormal
-		certificate = constants.PIACertificateNormal
+		certificate = constants.PiaCANormal
 	default: // strong
 		defaultCipher = constants.AES256cbc
 		defaultAuth = constants.SHA256
 		X509CRL = constants.PiaX509CRLStrong
-		certificate = constants.PIACertificateStrong
+		certificate = constants.PiaCAStrong
 	}
 
 	if len(settings.Ciphers) == 0 {

internal/provider/privateinternetaccess/portforward.go

@@ -15,7 +15,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/provider/utils"
 	"github.com/qdm12/golibs/format"
 )
@@ -33,7 +33,13 @@ var (
 func (p *PIA) PortForward(ctx context.Context, client *http.Client,
 	logger utils.Logger, gateway net.IP, serverName string) (
 	port uint16, err error) {
-	server := constants.PIAServerWhereName(p.servers, serverName)
+	var server models.PIAServer
+	for _, server = range p.servers {
+		if server.ServerName == serverName {
+			break
+		}
+	}
+
 	if !server.PortForward {
 		logger.Error("The server " + serverName +
 			" (region " + server.Region + ") does not support port forwarding")

internal/provider/privateinternetaccess/portforward_test.go

@@ -20,7 +20,7 @@ func Test_newHTTPClient(t *testing.T) {
 
 	const serverName = "testserver"
 
-	certificateBytes, err := base64.StdEncoding.DecodeString(constants.PIACertificateStrong)
+	certificateBytes, err := base64.StdEncoding.DecodeString(constants.PiaCAStrong)
 	require.NoError(t, err)
 	certificate, err := x509.ParseCertificate(certificateBytes)
 	require.NoError(t, err)