add Saving Events in DB

src/main/java/mops/gruppen2/domain/EventDTO.java

@@ -1,11 +1,14 @@
 package mops.gruppen2.domain;
 
+import lombok.Data;
 import lombok.Value;
+import org.springframework.data.annotation.Id;
 import org.springframework.data.relational.core.mapping.Table;
 
-@Value
 @Table("event")
+@Data
 public class EventDTO {
+    @Id
     long event_id;
     long group_id;
     String user_id;