WASI HTTP version

[vigoo]

We are building a platform (Golem) built on the WebAssembly system interface (WASI). Unfortunately reqwest at the moment does not support wasi-http (WASI's http interface), and although there are discussions and draft pull requests to introduce support for it, it does not look like it is going to happen anytime soon.
The most production ready Rust wrapper around wasi-http at the moment is the client in wstd that also includes a wasi compatible async runtime.

I've forked progenitor and made a wstd based version if it: https://github.com/golemcloud/progenitor-wasi-http

It has some serious limitations compared to the real version though, due to the limitations of wasi-http:

• no websocket upgrade
• no streaming (body and paging)
• more constrained requirements for what can be passed as a raw body

With all these limitations it's a very useful library for platforms based on wasi-http.

I would be happy to work on somehow making this part of the official library, but it's not straightforward at all, with reqwest completely replaced and all these other limitations introduced. Maybe it does not worth the effort; I primarily opened this issue to discuss this.
If there is interest in upstreaming it, let's discuss how; otherwise we can just keep it as a fork for now.

[ahl]

I think the discussion in #1272 may be relevant. I'd like to see us abstract the client interface away from reqwest with an implementation for reqwest (at least to start). If that's something you'd be interested in helping with, I think the first step would be to define an appropriate trait for the client.