Add post change log tracking

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

@@ -0,0 +1,17 @@
+package com.openisle.model;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Table;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Getter
+@Setter
+@NoArgsConstructor
+@Entity
+@Table(name = "post_closed_change_logs")
+public class PostClosedChangeLog extends PostChangeLog {
+    private boolean oldClosed;
+    private boolean newClosed;
+}