feat: implement medal feature

backend/src/main/java/com/openisle/controller/MedalController.java

@@ -0,0 +1,23 @@
+package com.openisle.controller;
+
+import com.openisle.dto.MedalDto;
+import com.openisle.service.MedalService;
+import lombok.RequiredArgsConstructor;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.List;
+
+@RestController
+@RequestMapping("/api/medals")
+@RequiredArgsConstructor
+public class MedalController {
+    private final MedalService medalService;
+
+    @GetMapping
+    public List<MedalDto> getMedals(@RequestParam(value = "userId", required = false) Long userId) {
+        return medalService.getMedals(userId);
+    }
+}