Re-evaluate reverse proxy implementation once `reqwest` has caught up with `hyper` and `axum`

[mbr]

An open PR adds direct conversion of incoming axum requests into reqwest ones. The discussion also links a draft PR that upgrades to hyper 1.0.

Overall this development should be monitored. rockslide currently does quite a few hacks in reverse_proxy (e.g. casting the method into a string and reparsing it), many of which are due to library incompatibilities (e.g. at the time of writing reqwest depended on http=^0.2 while axum already was on http=1. If these can be unified, the code of reverse_proxy::reverse_proxy could potentially be greatly simplified.