Before this change, if the server returned a 302 redirect message when
opening a file rclone would do the redirect but drop the
Authorization: header. This is a sensible thing to do for security
reasons but breaks some setups.
This patch adds the --webdav-auth-redirect flag which makes it
preserve the auth just for this kind of request.
See: https://forum.rclone.org/t/webdav-401-unauthorized-when-server-redirects-to-another-domain/39292
965bf19065