Establish WebSocket connection to Cloud (#35734)

This PR adds a new WebSocket connection to Cloud.

This connection will be used to push down notifications from the server
to the client.

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/cloud_api_client/src/cloud_api_client.rs

@@ -1,11 +1,19 @@
+mod websocket;
+
 use std::sync::Arc;
 
 use anyhow::{Context, Result, anyhow};
+use cloud_api_types::websocket_protocol::{PROTOCOL_VERSION, PROTOCOL_VERSION_HEADER_NAME};
 pub use cloud_api_types::*;
 use futures::AsyncReadExt as _;
+use gpui::{App, Task};
+use gpui_tokio::Tokio;
 use http_client::http::request;
 use http_client::{AsyncBody, HttpClientWithUrl, Method, Request, StatusCode};
 use parking_lot::RwLock;
+use yawc::WebSocket;
+
+use crate::websocket::Connection;
 
 struct Credentials {
     user_id: u32,
@@ -78,6 +86,41 @@ impl CloudApiClient {
         Ok(serde_json::from_str(&body)?)
     }
 
+    pub fn connect(&self, cx: &App) -> Result<Task<Result<Connection>>> {
+        let mut connect_url = self
+            .http_client
+            .build_zed_cloud_url("/client/users/connect", &[])?;
+        connect_url
+            .set_scheme(match connect_url.scheme() {
+                "https" => "wss",
+                "http" => "ws",
+                scheme => Err(anyhow!("invalid URL scheme: {scheme}"))?,
+            })
+            .map_err(|_| anyhow!("failed to set URL scheme"))?;
+
+        let credentials = self.credentials.read();
+        let credentials = credentials.as_ref().context("no credentials provided")?;
+        let authorization_header = format!("{} {}", credentials.user_id, credentials.access_token);
+
+        Ok(cx.spawn(async move |cx| {
+            let handle = cx
+                .update(|cx| Tokio::handle(cx))
+                .ok()
+                .context("failed to get Tokio handle")?;
+            let _guard = handle.enter();
+
+            let ws = WebSocket::connect(connect_url)
+                .with_request(
+                    request::Builder::new()
+                        .header("Authorization", authorization_header)
+                        .header(PROTOCOL_VERSION_HEADER_NAME, PROTOCOL_VERSION.to_string()),
+                )
+                .await?;
+
+            Ok(Connection::new(ws))
+        }))
+    }
+
     pub async fn accept_terms_of_service(&self) -> Result<AcceptTermsOfServiceResponse> {
         let request = self.build_request(
             Request::builder().method(Method::POST).uri(