- Check if it's part of the metadata through a function call rather than
checking `Base.metadata` in every single module.
- Make it possible to override them (mostly for doc generation logic
that needs to be able to import those classes).
- Make it possible to extend them.
- Support for cloud instances as native entities.
- Using Marshmallow dataclasses+schemas instead of custom `Response`
objects.
- Merge `linode` backend into `linode` plugin.