Build and send a multi upload request

gistfile1.txt

//Step 1: build and send a multi upload request
if (chunkIndex == 0)
{
    var initiateRequest = new InitiateMultipartUploadRequest
    {
        BucketName = bucketName,
        Key = fileName
    };

    var initResponse = _s3Client.InitiateMultipartUpload(initiateRequest);
    uploadId = initResponse.UploadId;
}