kio_http is dead, long live kio_http

Everything about the implementation is horrible. We need to do something about that.

Where do we actually need http support in KIO?

This used to be primarily Konqueror, but since Webengine that is no longer the case.

A bunch of places use KIO::get with HTTP for simple HTTP GET requests, that can easily be done using QtNetwork facilities.

There's the webdav worker that operates on top of kio_http, which is useful to browser your Nextcloud from Dolphin.

Then there's the use case of a generic KIO-using app, e.g. Kate, opening files from http URLs that way.

There's a lot of integration with systemsettings KCMs (Cache, connection preferences, cookies etc), but these are largely only relevant for browsers

We should look into replacing the internals of kio_http with something like QNetworkAccessManager or libcurl instead of our homegrown unmaintainable implementation