Replace isahc with async ureq (#18414)

REplace isahc with ureq everywhere gpui is used.

This should allow us to make http requests without libssl; and avoid a
long-tail of panics caused by ishac.

Release Notes:

- (potentially breaking change) updated our http client

---------

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/ureq_client/examples/client.rs

@@ -0,0 +1,24 @@
+use futures::AsyncReadExt;
+use http_client::{AsyncBody, HttpClient};
+use ureq_client::UreqClient;
+
+fn main() {
+    gpui::App::headless().run(|cx| {
+        println!("{:?}", std::thread::current().id());
+        cx.spawn(|cx| async move {
+            let resp = UreqClient::new(
+                None,
+                "Conrad's bot".to_string(),
+                cx.background_executor().clone(),
+            )
+            .get("http://zed.dev", AsyncBody::empty(), true)
+            .await
+            .unwrap();
+
+            let mut body = String::new();
+            resp.into_body().read_to_string(&mut body).await.unwrap();
+            println!("{}", body);
+        })
+        .detach();
+    })
+}