Add the support to send image files directly using multipart/form-data instead of application/x-www-form-urlencoded

[klalit]

This avoids the need to read and base64 encode the image prior to REST api call. It will be useful for models that take file/image as input for e.g. model for the image classification or ocr.

A detailed discussion in the context

https://stackoverflow.com/questions/4007969/application-x-www-form-urlencoded-or-multipart-form-data

microsoft also uses this MIME type for the images

https://westus.dev.cognitive.microsoft.com/docs/services/56f91f2d778daf23d8ec6739/operations/56f91f2e778daf14a499e1fe

[klalit]

functionality implemented and merged