Closes #13427: Public model registration (#14152)

* Initial work on #13427

* Clarify documentation

* Reference public models registry when populating models for ConfigTemplate context

netbox/dcim/models/cables.py

@@ -431,6 +431,8 @@ class CablePath(models.Model):
     )
     _nodes = PathField()
 
+    _netbox_private = True
+
     class Meta:
         verbose_name = _('cable path')
         verbose_name_plural = _('cable paths')