Create a net::HttpAuthHandlerRegistryFactory like Chromium

Instead of creating a "default" HttpAuthHandlerFactory, create a
HttpAuthHandlerRegistryFactory which should have the ability to use
multiple different authentication schemes, similar to what Chromium
does.

Task-number: QTBUG-57729
Change-Id: I4486e2280838b002a9badb6d4261676199045f4b
Reviewed-by: Michal Klocek <michal.klocek@qt.io>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>