feat: add poll post type

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

@@ -0,0 +1,16 @@
+package com.openisle.dto;
+
+import lombok.Data;
+
+import java.time.LocalDateTime;
+import java.util.List;
+import java.util.Map;
+
+@Data
+public class PollDto {
+    private String question;
+    private List<String> options;
+    private Map<Integer, Integer> votes;
+    private LocalDateTime endTime;
+    private List<AuthorDto> participants;
+}