Provide user agent when performing HTTP requests (#15470)

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/collab/src/rpc.rs

@@ -995,7 +995,8 @@ impl Server {
             tracing::Span::current().record("connection_id", format!("{}", connection_id));
             tracing::info!("connection opened");
 
-            let http_client = match IsahcHttpClient::new() {
+            let user_agent = format!("Zed Server/{}", env!("CARGO_PKG_VERSION"));
+            let http_client = match IsahcHttpClient::builder().default_header("User-Agent", user_agent).build() {
                 Ok(http_client) => Arc::new(http_client),
                 Err(error) => {
                     tracing::error!(?error, "failed to create HTTP client");