fix: initialize notification frequency

AoU-Model/src/main/java/ch/unige/aou/model/settings/PersonNotificationType.java

@@ -36,6 +36,7 @@ public class PersonNotificationType extends CompositeResource<PersonNotification
 
   public PersonNotificationType() {
     this.compositeResId = new PersonNotificationTypeId();
+    this.notificationFrequency = Frequency.DAILY;
   }
 
   @Override