Serializer field "createdAt" of layers and featuretypes is null

[lvgl-oh]

Steps to Reproduce

1. Register a WMS or WFS

Expected Behavior

the field createdAt of Layers or FeatureTypes shows the point in time when the Service was added

Observed Behavior

the createdAt field is empty

[jokiefer]

Our PersistenceHandler does not currently handle history models during bulk creation.

The django-simple-history documentation on bulk creating and queryset updating needs to be reviewed, and a solution for handling custom bulk creation across multiple models needs to be developed.