Expose uwr

[onedayitwillmake]

As a user, some things would be easier if the underlying UnityWebRequest object was available or supplied to the Next function.

For example, there does not appear to be a way to inspect the request headers after a successful request.

[onedayitwillmake]

@monry

[onedayitwillmake]

A current work around is as follows:

        var req = new UnityWebRequest($"/api/whatever", "POST");
        req.ApplyRequestHeader("Content-Type", "application/json;charset=UTF-8");
        req.ApplyRequestBody("{}");
        req.ApplyDownloadHandler(new DownloadHandlerBuffer());
        req.SendWebRequestAsObservable().Select( _ => req).Subscribe(req => {
            
        });