* update http2 config due to deprecation

the previous way to let `http2` follow a `listen` was depracated, it
moved to `http2 on;`

* enable quic and http3

I hope the comments are somewhat understandable. if someone can describe
the `reuseport` part more concise, please do.

Updated the 'nginx reverse-proxy fronting' documentation with a guide for Nginx Proxy Manager, as you can't use the pre-existing nginx matrix.conf