Feat: multiple OpenVPN ciphers for negotiation

- Perfect privacy to accept AES-256-CBC and AES-256-GCM
- Cyberghost default cipher set to AES-256-GCM
- `OPENVPN_CIPHER` accept comma separated cipher values
- Use `ncp-ciphers` for OpenVPN 2.4

internal/provider/utils/cipher.go

@@ -1,17 +1,22 @@
 package utils
 
 import (
+	"strings"
+
 	"github.com/qdm12/gluetun/internal/constants"
 )
 
-func CipherLines(cipher, version string) (lines []string) {
+func CipherLines(ciphers []string, version string) (lines []string) {
 	switch version {
 	case constants.Openvpn24:
-		return []string{"cipher " + cipher}
+		return []string{
+			"cipher " + ciphers[0],
+			"ncp-ciphers " + strings.Join(ciphers, ":"),
+		}
 	default: // 2.5 and above
 		return []string{
-			"data-ciphers-fallback " + cipher,
-			"data-ciphers " + cipher,
+			"data-ciphers-fallback " + ciphers[0],
+			"data-ciphers " + strings.Join(ciphers, ":"),
 		}
 	}
 }