public async Task <IActionResult> OnPostUploadAsync(string id, [FromForm] IFormFile upload)
        {
            if (!ModelState.IsValid)
            {
                return(RedirectToPage());
            }

            if (upload != null)
            {
                var openReadStream = upload.OpenReadStream();
                await _manager.AddRevisionAsync(User, id, upload.FileName, openReadStream);
            }

            return(RedirectToPage());
        }