MM-27178: Use FileSettings.Directory in export tool (#15100)

* MM-27178: use FileSettings.Directory in export

* Set empty FileSettings.Directory to default value

* Validate that FileSettings.Directory is non-empty

* Don't set FileSettings.Directory to / in fixConfig

* Run make i18n-extract

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/config.go

@@ -1280,7 +1280,7 @@ func (s *FileSettings) SetDefaults(isUpdate bool) {
 		s.DriverName = NewString(IMAGE_DRIVER_LOCAL)
 	}
 
-	if s.Directory == nil {
+	if s.Directory == nil || *s.Directory == "" {
 		s.Directory = NewString(FILE_SETTINGS_DEFAULT_DIRECTORY)
 	}
 
@@ -3018,6 +3018,10 @@ func (s *FileSettings) isValid() *AppError {
 		return NewAppError("Config.IsValid", "model.config.is_valid.file_salt.app_error", nil, "", http.StatusBadRequest)
 	}
 
+	if *s.Directory == "" {
+		return NewAppError("Config.IsValid", "model.config.is_valid.directory.app_error", nil, "", http.StatusBadRequest)
+	}
+
 	return nil
 }