title: How to set custom header on form-data item?
body: <p>I am sending a multipart data from a nodeJS route as a response.
  I used <code>form-data</code> library to accomplish, my requirement is to send additional header information for all binary data.</p>
  
  <p>I tried the following</p>
  
  <pre><code> router.get('/getdata', async (req, res, next) =&gt; {
      var form = new FormData();
      var encodedImage2 = fs.readFileSync('./public/image2.png');
  
      var CRLF = '\r\n';
      var options = {
          header: CRLF + '--' + form.getBoundary() + CRLF + 'X-Custom-Header: 123' + CRLF + CRLF
      };
      form.append('image2.png', encodedImage2, options);
  
      res.set('Content-Type', 'multipart/form-data; boundary=' + form.getBoundary());
      form.pipe(res);
   });
  
  </code></pre>
  
  <p>in the output I get only the header </p>
  
  <pre><code>X-Custom-Header: 123
  </code></pre>
  
  <p>without the <code>option</code> object I can get </p>
  
  <pre><code>Content-Disposition: form-data; name="image2.png"
  Content-Type: application/octet-stream
  </code></pre>
  
  <p>I need an output headers something like</p>
  
  <pre><code>Content-Disposition: form-data; name="image2.png"
  Content-Type: application/octet-stream
  X-custom-Header: 123
  </code></pre>