feat: implement lottery post type

backend/src/main/java/com/openisle/model/LotteryPost.java

@@ -0,0 +1,46 @@
+package com.openisle.model;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+import java.time.LocalDateTime;
+import java.util.HashSet;
+import java.util.Set;
+
+@Entity
+@Table(name = "lottery_posts")
+@Getter
+@Setter
+@NoArgsConstructor
+@PrimaryKeyJoinColumn(name = "post_id")
+public class LotteryPost extends Post {
+
+    @Column
+    private String prizeDescription;
+
+    @Column
+    private String prizeIcon;
+
+    @Column(nullable = false)
+    private int prizeCount;
+
+    @Column
+    private LocalDateTime startTime;
+
+    @Column
+    private LocalDateTime endTime;
+
+    @ManyToMany
+    @JoinTable(name = "lottery_participants",
+            joinColumns = @JoinColumn(name = "post_id"),
+            inverseJoinColumns = @JoinColumn(name = "user_id"))
+    private Set<User> participants = new HashSet<>();
+
+    @ManyToMany
+    @JoinTable(name = "lottery_winners",
+            joinColumns = @JoinColumn(name = "post_id"),
+            inverseJoinColumns = @JoinColumn(name = "user_id"))
+    private Set<User> winners = new HashSet<>();
+}