feat: Pub/Sub 기반 WebSocket 서버 구성

resolve: #33

src/main/java/univ/goormthon/kongju/domain/chat/controller/ChatController.java

@@ -0,0 +1,18 @@
+package univ.goormthon.kongju.domain.chat.controller;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.messaging.handler.annotation.MessageMapping;
+import org.springframework.messaging.simp.SimpMessagingTemplate;
+import org.springframework.stereotype.Controller;
+
+@Controller
+@RequiredArgsConstructor
+public class ChatController {
+
+    private final SimpMessagingTemplate template;
+    @MessageMapping("/chat")
+    public void sendMessage(String message) {
+        this.template.convertAndSend("/sub", message);
+    }
+
+}