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/reqwest_client/examples/client.rs

@@ -0,0 +1,16 @@
+use futures::AsyncReadExt as _;
+use http_client::AsyncBody;
+use http_client::HttpClient;
+use reqwest_client::ReqwestClient;
+
+#[tokio::main]
+async fn main() {
+    let resp = ReqwestClient::new()
+        .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);
+}