Please support withCredentials property

## 🚀 Feature Requests

CachedNetworkImage supports running on Flutter for web. Images are fetched using an XHR request.
Sometimes it is necessary to authenticate a request with a session id within a cookie header.

In a Cross-Origin environment (flutter frontend has been loaded from a different hostname than the image is loaded from) the browser does not pass cookie headers for XHR requests because by default the flag `withCredentials` is false.

Please support an optional parameter `withCredentials` for CachedNetworkImage.

Dart supports this flag for dart:html:HttpRequest
https://api.dart.dev/stable/2.13.4/dart-html/HttpRequest/withCredentials.html

### Platforms affected (mark all that apply)
- [x] :all: web