15794 Make "related objects" dynamic

[alehaa]

Fixes: #15794

Instead of hardcoding relationships between models for the detail view, they are now dynamically generated.

Known limitations

1. If a related model doesn't have a list view, rendering of the related objects pane will fail. This limitation was already present before, but related models listed were explicitly chosen to do so. For all views shipped with NetBox I've added a filter if needed (omit parameter). However, external plugins might trigger this unintentionally, when named view is not available, but the relationship has not been setup with related_name='+' parameter. Switching to verified_view in the panel's template should resolve this, but might decrease performance slightly.

2. If a model introduces several relations to another model, they will all be listed with the same model name but different URL query parameters. This is not the case for models included in NetBox. As before, plugin developers can still use an extra panel for this special purpose and extra context about the different types of relationships.

[jeremystretch]

What is the purpose of this method? It seems like maybe a hook for monkey patching, which IMO should be discouraged. If needed, we could potentially extend the underlying get_related_models() utility function (not the class method) to collect additional types of relationships.

Or, if it's intended to be overridden naturally, we could introduce an extra keyword argument to the get_related_models() method to pass these.

[alehaa]

You are right, its intended to be used as a hook by view classes, e.g. when not only direct relations should be collected.

Although I prefer a generic approach that implements some logic in the utility function, I don't know how we should determine which transient relations are interesting for object views. So for now, I'd remove this method and add an extra keyword argument to the class method instead.