Provide user agent when performing HTTP requests (#15470)

Release Notes:

- N/A

---------

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

crates/semantic_index/examples/index.rs

@@ -26,7 +26,7 @@ fn main() {
         });
 
         let clock = Arc::new(FakeSystemClock::default());
-        let http = Arc::new(HttpClientWithUrl::new("http://localhost:11434", None));
+        let http = Arc::new(HttpClientWithUrl::new("http://localhost:11434", None, None));
 
         let client = client::Client::new(clock, http.clone(), cx);
         Client::set_global(client.clone(), cx);