feat: implement lottery post type

backend/src/main/java/com/openisle/dto/LotteryDto.java

@@ -0,0 +1,17 @@
+package com.openisle.dto;
+
+import lombok.Data;
+import java.time.LocalDateTime;
+import java.util.List;
+
+/** Metadata for lottery posts. */
+@Data
+public class LotteryDto {
+    private String prizeDescription;
+    private String prizeIcon;
+    private int prizeCount;
+    private LocalDateTime startTime;
+    private LocalDateTime endTime;
+    private List<AuthorDto> participants;
+    private List<AuthorDto> winners;
+}