Add an option to customize the error messages shown in the SfFileManager upload dialog. Specifically, allow replacing the generic “File failed to upload” message with a custom message returned by the provider when an upload fails.
Use case: When an upload operation fails, the provider should be able to return a meaningful, user-friendly error message (e.g., quota exceeded, invalid file type, virus detected), and SfFileManager should display that message in the upload dialog instead of the default generic error message.