🐛 공지사항 등록시 id가 빈문자열로 등록되는 bug fix

infrastructure/datastore-mongodb-reactive/src/main/kotlin/me/jiniworld/demohx/persistence/notice/NoticeDocument.kt

@@ -7,13 +7,9 @@ import org.springframework.data.mongodb.core.mapping.Document
 import java.time.LocalDateTime
 
 @Document(value = "notice")
-internal class NoticeDocument {
+internal class NoticeDocument(var title: String, var content: String) {
     @Id
-    var id: String = ""
-
-    var title: String = ""
-
-    var content: String = ""
+    var id: String? = null
 
     @CreatedDate
     var createdAt: LocalDateTime = LocalDateTime.now()