feat(http-server): Add WASI reactor support to http-server cap

[Mossaka]

This PR switches the WASI command model to reactor model for wasi-http. The reason for that is in the command model, each exported HTTP handler function would not be able to initialize properly with the WASI stdout because the host will not invoke _start. The reactor solves this issue.

Breaking changes

1. rust slight applications that use http-server must use cargo new --lib to create the rust program, instead of --bin. This will create a rust library. In Cargo.toml, the following attribute is needed:

[lib]
crate-type = ["cdylib"]

2. Use slight provided slight_http_server_macro::on_server_init macro on top of the router and server setup function.

A rust slight program that uses http-server capability would end up looking like

use http_server::*;
use slight_http_handler_macro::register_handler;
use slight_http_server_macro::on_server_init;

wit_bindgen_rust::import!("../../wit/http-server.wit");
wit_bindgen_rust::export!("../../wit/http-server-export.wit");
wit_bindgen_rust::import!("../../wit/http-client.wit");
wit_error_rs::impl_error!(http_server::HttpRouterError);
wit_error_rs::impl_error!(http_client::HttpError);

#[on_server_init]
fn main() -> Result<()> {
    let router = Router::new()?;
    let router_with_route = router
        .get("/hello", "handle_hello")?
        .get("/person/:name", "handle_person_with_name")?
        .get("/foo", "handle_foo")?
        .put("/bar", "handle_bar")?
        .post("/upload", "upload")?
        .delete("/delete-file", "delete_file_handler")?
        .get("/request", "handle_request")?;

    println!("guest starting server");
    let _ = Server::serve("0.0.0.0:3000", &router_with_route)?;
    // server.stop().unwrap();
    println!("guest moving on");

    Ok(())
}

A Note to Reviewers

I've tested that the http handler would work with keyvalue capability correctly. I still need to add more docs to this newly added macro and changes to the slight runtime library, but other than that, this PR is ready to review.

[devigned]

lgtm! I've tested it in deislabs/containerd-wasm-shims#80 and pods are displaying log messages from the HTTP handlers.

I'm good with pulling this in and having a follow up PR for docs. Up to you, @Mossaka.