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>

i18n/en.json

@@ -5722,6 +5722,10 @@
     "id": "model.config.is_valid.data_retention.message_retention_days_too_low.app_error",
     "translation": "Message retention must be one day or longer."
   },
+  {
+    "id": "model.config.is_valid.directory.app_error",
+    "translation": "Invalid Local Storage Directory. Must be a non-empty string."
+  },
   {
     "id": "model.config.is_valid.display.custom_url_schemes.app_error",
     "translation": "The custom URL scheme {{.Scheme}} is invalid. Custom URL schemes must start with a letter and contain only letters, numbers, plus (+), period (.) and hyphen (-)."