AbstractNetworkJob: Improve redirect handling #5555

AbstractNetworkJob: Improve redirect handling #5555

* For requests:
  - reuse the original QNetworkRequest, so headers and attributes
    are the same as in the original request
  - determine the original http method from the reply and the request
    attributes
  - keep the original request body around such that it can be sent
    again in case the request is redirected

* Simplify the interface that is used for creating new requests in
  AbstractNetworkJob.