Trying to run the `janus` Rust `gst-example`, `tungstenite` reports:
> Missing, duplicated or incorrect header sec-websocket-key
Indeed, all mandatory headers from the following list are missing
(code from `tungstenite:🤝:client::generate_request`):
```rust
const WEBSOCKET_HEADERS: [&str; 5] =
["Host", "Connection", "Upgrade", "Sec-WebSocket-Version", KEY_HEADERNAME];
```
These headers are mandatory for the websocket handshake. This feature is
selected by async-tungstenite.
Prior to this commit, the HTTP request was created with the header
"Sec-WebSocket-Protocol" only. Delegating the request creation to tungstenite
adds the missing headers.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4240>
