The implementation for custom saving is too redundant

[jsakamotoIGJP]

https://github.dev/jsakamotoIGJP/Documentation/blob/6bed33b86ea21450fd2c47c4cd2b05037fc0aa73/docs/web/saving-dashboards.md#L252-L262

• It will be better to use the "Declarative Using".
• It will be better to copy from the request body stream to the FileStream directly without a byte[] buffer.

From:

    byte[] bytes;
    using (var ms = new MemoryStream())
    {
        await request.Body.CopyToAsync(ms);
        bytes = ms.ToArray();
    }

    using (var stream = File.Open(filePath, FileMode.Open))
    {
        stream.Write(bytes, 0, bytes.Length);
    }

To:

    using var stream = File.Open(filePath, FileMode.Open);
    await request.Body.CopyToAsync(stream);