refactor: 리뷰 반영4

- 비즈니스 로직 에러와 DB접근에러 시 http 상태코드를 500이 아닌 400을 반환하도록 수정

src/main/java/wooteco/subway/admin/controller/GlobalDefaultExceptionHandler.java

@@ -23,7 +23,7 @@ protected ResponseEntity<ErrorResponse> handleMethodArgumentNotValidException(
     @ExceptionHandler({BusinessException.class, DataAccessException.class})
     protected ResponseEntity<ErrorResponse> handleBusinessException(final Exception e) {
         final ErrorResponse response = new ErrorResponse(e.getMessage());
-        return new ResponseEntity<>(response, HttpStatus.INTERNAL_SERVER_ERROR);
+        return new ResponseEntity<>(response, HttpStatus.BAD_REQUEST);
     }
 
     @ExceptionHandler(Exception.class)