JS bindings should include `io` functionality

[spacebear21]

Due to WASM limitations the io feature is disabled in JS auto-generated bindings. We should consider whether to offer an alternative for fetching OHTTP keys in JS bindings, at a minimum just documenting how to fetch keys with the fetch API.

[DanGould]

This could be a good first issue because it's well defined for someone who understands HTTP, WebSocket, and TLS clients, but it definitely has some sharp edges. The thing is this issue is implementing a solution that has already been proven in Mutiny ages ago.

The thing is with NodeJS you can probably use the HTTPS client to do CONNECT requests and nest the bootstrap fetch OHTTP keys messages. If NodeJS has the HTTPS client, it may already have a viable TLS client available there to do the nested TLS.

However, in the browser, I'm not sure CONNECT requests are available with the fetch API. Nor is a TLS client API available on any such CONNECT client or shipped made available to JavaScript. So I would include rustls to nest TLS in the example and then if CONNECT can't work I'd use the directory's WebSocket API instead to bootstrap and close this issue.