refactor: 클래스명 변경

src/main/java/com/softeer/backend/bo_domain/admin/controller/MainPageController.java → src/main/java/com/softeer/backend/bo_domain/admin/controller/AdminMainPageController.java

@@ -11,7 +11,7 @@
 @RestController
 @RequiredArgsConstructor
 @RequestMapping("/admin")
-public class MainPageController {
+public class AdminMainPageController {
     private final MainPageService mainPageService;
 
     @GetMapping("/main")