QtHttpServer is missing the possibility to handle multipart bodies

Most of the time multi-part is used because to handle big data upload/download.

Since multi-part requests are handled completly handled internally by QHttpServerRequest, there is no way to stream data directly to "something" (i.e a file).

I don't look at QHttpServerResponse but the same feature should be added as well, with the same goal, be able to handle hudge data chunks.