MailJson 타입으로 추가생성

src/main/java/com/caliverse/admin/dynamodb/entity/MailItem.java

@@ -5,11 +5,13 @@ import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Data;
 import lombok.NoArgsConstructor;
+import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbBean;
 
 @Data
 @Builder
 @NoArgsConstructor
 @AllArgsConstructor
+@DynamoDbBean
 public class MailItem {
     @JsonProperty("ItemId")
     private Integer itemId;