…2387)

Implements the `websocket` protocol upgrade in iroh-relay and changes
`iroh-net` clients to connect with `websocket` instead of `iroh derp
http`.

State of this is:
- `cargo test -p iroh-net` runs green
- websocket on the relay is supported
- backwards compatibility is tested
- the client also supports connecting using websockets
- (but we're forced to use tungstenites connection establishment, no
custom `MaybeTlsStream`.)
  - It decides this via the URL scheme (`ws(s)://` vs. `http(s)://`) 

TODO:
- [x] Enumify the client so it's possible to keep using the old relay
protocol
- [x] Cleanup!
- [x] Some perf TODOs in the server, less copying.
- [x] Update documentation (e.g. `local_addr` having another case being
`None`)
- [x] Add metrics for websocket-accept & derp-accept counts
- [x] Snapshot tests (using `parse_hexdump`) for "new" wire format

## Description

- Supports clients connecting to iroh-relay with websockets & running
the derp protocol over websocket `Binary` msgs.
- Adds support for the relay answering `Upgrade: websocket` headers
instead of `Upgrade: iroh derp http` appropriately.
- Adds support for `ClientBuilder` to dial via websockets, if the relay
URL is set with a `ws`/`wss` URL scheme.

## Breaking Changes

- Not in the protocol: The old HTTP upgrade & protocol should still be
supported. There's tests to ensure this.
- `Client::local_addr` will now also return `None`, if one connected
using websockets.
- `iroh_net::relay::http::ClientError`: Added a variant `WebsocketError`
for errors when establishing a connection using websockets.

## Notes & open questions

Closes #2370 

## Change checklist

- [x] Self-review.
- [x] Documentation updates if relevant.
- [x] Tests if relevant.
- [x] All breaking changes documented.