Support HTTP proxies in clients connecting to relays over websockets

[matheus23]

At the moment, iroh clients that connect to a relay via websockets do so using the tokio_tungstenite_wasm library, which doesn't support providing your own AsyncRead/AsyncWrite, so you're not in control of connection establishment (which makes sense because in the browser you don't have control over that).

We should vendor the WebSocketStream library used in tokio_tungstenite_wasm and add our own enum case for a connection where we do provide our own AsyncRead/AsyncWrite (MaybeTlsStreamReader/Writer specifically) and have control over connection establishment.

This enables:

• HTTP proxy support when connecting to a relay over websockets
• Writing tests that excercise relay-over-WSS (with TLS, but faked certificates)

Context: #2387 (comment)

[matheus23]

I'd say this is somewhat blocked on migrating away from tokio_tungstenite_wasm (see the linked comment in the issue).

Currently I'm waiting for denoland/fastwebsockets#78 to be merged.