Add service_is_ready() (#339)

* Add check if service is ready

* Update changelog

* Fix unneeded return

---------

Co-authored-by: carter <carterjschultz@gmail.com>
Co-authored-by: carter <carter@amprobotics.com>

Author: 3 people

rclrs/minimal_client_service/src/minimal_client.rs

@@ -13,7 +13,9 @@ fn main() -> Result<(), Error> {
 
     println!("Starting client");
 
-    std::thread::sleep(std::time::Duration::from_millis(500));
+    while !client.service_is_ready()? {
+        std::thread::sleep(std::time::Duration::from_millis(10));
+    }
 
     client.async_send_request_with_callback(
         &request,

rclrs/minimal_client_service/src/minimal_client_async.rs

@@ -12,7 +12,9 @@ async fn main() -> Result<(), Error> {
 
     println!("Starting client");
 
-    std::thread::sleep(std::time::Duration::from_millis(500));
+    while !client.service_is_ready()? {
+        std::thread::sleep(std::time::Duration::from_millis(10));
+    }
 
     let request = example_interfaces::srv::AddTwoInts_Request { a: 41, b: 1 };