add a new property Name to MultipartItem class

[javirszhang]

consider following suituation, my webapi get upload files from Request.Form.Files so that IFormFile.Name is very important.

[HttpPost("upload/{bucket}")]
public ApiResult<List<FileUploadResponseDTO>> FileUpload(string bucket)
{
    List<FileUploadResponseDTO> list = new List<FileUploadResponseDTO>();
    MediaFileUploadProvider mediaFile = new MediaFileUploadProvider(bucket);
    foreach (var file in Request.Form.Files)
    {
        var fileDTO = mediaFile.Execute(file.Name, file.FileName, file.OpenReadStream());
        if (fileDTO != null)
        {
            list.Add(fileDTO);
        }
    }
    return list;
}

IFormFile.Name determins file means, it can not use a fixed parameter name.

What kind of change does this PR introduce?
enhancement, let users can set Content-Disposition name attribute when necessary.

What is the current behavior?
Always use the parameter name as the Content-Disposition name attribute.

What is the new behavior?
Add a new property Name to MultipartItem class, so we can set it when necessary.

What might this PR break?
nothing

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

[dnfadmin]

All CLA requirements met.

[clairernovotny]

Included in #1002

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.