Add simple healthcheck (#291)

crates/y-sweet/src/server.rs

@@ -336,6 +336,7 @@ impl Server {
 
     pub fn routes(self: &Arc<Self>) -> Router {
         Router::new()
+            .route("/ready", get(ready))
             .route("/check_store", get(check_store))
             .route("/doc/ws/:doc_id", get(handle_socket_upgrade))
             .route("/doc/new", post(new_doc))
@@ -572,6 +573,11 @@ async fn check_store(
     Ok(Json(json!({"ok": true})))
 }
 
+/// Always returns a 200 OK response, as long as we are listening.
+async fn ready() -> Result<Json<Value>, AppError> {
+    Ok(Json(json!({"ok": true})))
+}
+
 async fn new_doc(
     authorization: Option<TypedHeader<headers::Authorization<headers::authorization::Bearer>>>,
     State(server_state): State<Arc<Server>>,