feat/Created new NotificationDTO entity

src/main/java/no/ntnu/idi/stud/savingsapp/dto/notification/NotificationDTO.java

+package no.ntnu.idi.stud.savingsapp.dto.notification;
+
+import java.sql.Timestamp;
+import lombok.Data;
+import no.ntnu.idi.stud.savingsapp.model.notification.NotificationType;
+
+@Data
+public class NotificationDTO {
+
+  private long id;
+  private String message;
+  private boolean unread;
+  private NotificationType notificationType;
+  private Timestamp createdAt;
+
+}