Replace @controller with @RestController in MainController

The @controller annotation was replaced with @RestController in MainController.java file. This change allows the controller to automatically serialize the response objects into JSON, simplifying the controller's implementation by removing the need to manually handle the serialization.

messaging/consumer/src/main/java/nawaphon/microservices/event_sourcing/consumer/controllers/MainController.java

@@ -14,15 +14,15 @@
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.kafka.annotation.KafkaListener;
-import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.client.RestTemplate;
 
 import java.util.UUID;
 
-@Controller
+@RestController
 public class MainController {
 
     private static final Logger logger = LoggerFactory.getLogger(MainController.class);