Request to add customizable form-data name

[fumpierrez]

I think it would be nice to allow the Upload method to receive a custom name for the HTTP Form variable. Currently, I can't find a way to change the hard-coded name="file"

Example of actual request:
...Content-Disposition: form-data; name="file"; filename="IMG_20171231_185954.jpg"...

APIs and Forms already deployed, they might be expecting a different name there