removes the ConsoleRedirect backend from the main auth::Backends enum,
copy-paste the existing crate::proxy::task_main structure to use the
ConsoleRedirectBackend exclusively.
This makes the logic a bit simpler at the cost of some fairly trivial
code duplication.
preliminary for #9270
The auth::Backend didn't need to be in the mega ProxyConfig object, so I
split it off and passed it manually in the few places it was necessary.
I've also refined some of the uses of config I saw while doing this
small refactor.
I've also followed the trend and make the console redirect backend it's
own struct, same as LocalBackend and ControlPlaneBackend.
