Closes #13427: Public model registration (#14152)

* Initial work on #13427

* Clarify documentation

* Reference public models registry when populating models for ConfigTemplate context

netbox/core/models/data.py

@@ -378,6 +378,8 @@ class AutoSyncRecord(models.Model):
         fk_field='object_id'
     )
 
+    _netbox_private = True
+
     class Meta:
         constraints = (
             models.UniqueConstraint(