Add WASI HTTP example

[kate-goldenring]

The book is lacking in an example and more documentation on using WASI HTTP to create Wasm services and running them with cargo serve and wasmtime serve etc. Instead of writing and maintaining an example, @yoshuawuyts has started the process of upstreaming his wasi:http Rust sample to the BA. We should create a section with this new example. Ideally, we can show composition with this component too with registries