feat(health): Expose HealthService publically (#930)

tonic-health/src/server.rs

@@ -103,7 +103,9 @@ impl HealthReporter {
     }
 }
 
-struct HealthService {
+/// A service providing implementations of gRPC health checking protocol.
+#[derive(Debug)]
+pub struct HealthService {
     statuses: Arc<RwLock<HashMap<String, StatusPair>>>,
 }