Maint: refactor VPN configuration structure

- Paves the way for Wireguard
- VPN struct contains Type, Openvpn and Provider configurations
- OpenVPN specific options (e.g. client key) moved from Provider to Openvpn configuration struct
- Move Provider configuration from OpenVPN configuration to VPN
- HTTP control server returns only openvpn settings (not provider settings)

internal/configuration/vpnunlimited.go

@@ -28,10 +28,6 @@ func (settings *Provider) vpnUnlimitedLines() (lines []string) {
 		lines = append(lines, lastIndent+"Stream servers only")
 	}
 
-	if settings.ExtraConfigOptions.ClientKey != "" {
-		lines = append(lines, lastIndent+"Client key is set")
-	}
-
 	return lines
 }
 
@@ -48,16 +44,6 @@ func (settings *Provider) readVPNUnlimited(r reader) (err error) {
 		return err
 	}
 
-	settings.ExtraConfigOptions.ClientKey, err = readClientKey(r)
-	if err != nil {
-		return err
-	}
-
-	settings.ExtraConfigOptions.ClientCertificate, err = readClientCertificate(r)
-	if err != nil {
-		return err
-	}
-
 	settings.ServerSelection.Countries, err = r.env.CSVInside("COUNTRY", constants.VPNUnlimitedCountryChoices())
 	if err != nil {
 		return fmt.Errorf("environment variable COUNTRY: %w", err)
@@ -85,3 +71,17 @@ func (settings *Provider) readVPNUnlimited(r reader) (err error) {
 
 	return nil
 }
+
+func (settings *OpenVPN) readVPNUnlimited(r reader) (err error) {
+	settings.ClientKey, err = readClientKey(r)
+	if err != nil {
+		return err
+	}
+
+	settings.ClientCrt, err = readClientCertificate(r)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}