fix(helm) allow settings to be saved offline EE-1907 (#5907)

* allow settings to be saved offline.  Due to helm repo validation not working for bitnami when offline!

* @hookenz
dont validate the helm repo if the repo hasn't changed or is the default

api/http/handler/settings/settings_update.go

@@ -54,11 +54,8 @@ func (payload *settingsUpdatePayload) Validate(r *http.Request) error {
 	if payload.TemplatesURL != nil && *payload.TemplatesURL != "" && !govalidator.IsURL(*payload.TemplatesURL) {
 		return errors.New("Invalid external templates URL. Must correspond to a valid URL format")
 	}
-	if payload.HelmRepositoryURL != nil && *payload.HelmRepositoryURL != "" {
-		err := libhelm.ValidateHelmRepositoryURL(*payload.HelmRepositoryURL)
-		if err != nil {
-			return errors.Wrap(err, "Invalid Helm repository URL. Must correspond to a valid URL format")
-		}
+	if payload.HelmRepositoryURL != nil && *payload.HelmRepositoryURL != "" && !govalidator.IsURL(*payload.HelmRepositoryURL) {
+		return errors.New("Invalid Helm repository URL. Must correspond to a valid URL format")
 	}
 	if payload.UserSessionTimeout != nil {
 		_, err := time.ParseDuration(*payload.UserSessionTimeout)
@@ -114,7 +111,16 @@ func (handler *Handler) settingsUpdate(w http.ResponseWriter, r *http.Request) *
 	}
 
 	if payload.HelmRepositoryURL != nil {
-		settings.HelmRepositoryURL = strings.TrimSuffix(strings.ToLower(*payload.HelmRepositoryURL), "/")
+		newHelmRepo := strings.TrimSuffix(strings.ToLower(*payload.HelmRepositoryURL), "/")
+
+		if newHelmRepo != settings.HelmRepositoryURL && newHelmRepo != portainer.DefaultHelmRepositoryURL {
+			err := libhelm.ValidateHelmRepositoryURL(*payload.HelmRepositoryURL)
+			if err != nil {
+				return &httperror.HandlerError{http.StatusBadRequest, "Invalid Helm repository URL. Must correspond to a valid URL format", err}
+			}
+		}
+
+		settings.HelmRepositoryURL = newHelmRepo
 	}
 
 	if payload.BlackListedLabels != nil {