Enable the runtime feature of hyper when using tokio

[paolobarbolini]

Motivation

Currently axum never enables the runtime feature of hyper, which gates functions like Server::http1_header_read_timeout

Solution

This makes axum enable the runtime feature. The alternative is to import hyper and enable the feature but then Rust Analyzer imports things from hyper instead of axum, which is very annoying.

[davidpdrsn]

I'm not sure. Feels to me like axum should only enable the features that are necessary to use axum, or very common (such as h2.)

The alternatives sound fine to me.

[davidpdrsn]

@jplatte what do you think? I don't have any strong feelings about it. Its all gonna change for hyper 1.0 anyway :P

[jplatte]

Well since the runtime feature is described as

Enables convenient integration with tokio, providing connectors and acceptors for TCP, and a default executor.

and this is about what features our own tokio dependency activates, it seems fine to me.

[davidpdrsn]

Alright. Then lets just get it in 😊

@paolobarbolini merging main should fix CI and do you wanna add a changelog entry as well?