further refactor of eventhandling

Co-Authored-By: Talha Caliskan <killerber4t@users.noreply.github.com>
Co-Authored-By: tomvahl <tomvahl@users.noreply.github.com>
Co-Authored-By: xxnitram <xxnitram@users.noreply.github.com>
Co-Authored-By: kasch309 <kasch309@users.noreply.github.com>

src/main/java/mops/gruppen2/domain/event/AddUserEvent.java

@@ -24,7 +24,8 @@ public class AddUserEvent extends Event {
         this.email = email;
     }
 
-    public void apply(Group group, User user) {
+    public void apply(Group group) {
+        User user = new User(this.user_id, this.givenname, this.familyname, this.email);
         group.getMembers().add(user);
     }
 }