Sphinx config should not store custom class instances

No custom classes should be stored to the configuration.
Same reasoning as in https://github.com/eclipse-score/docs-as-code/issues/288.

```
WARNING: Unsupported type at 'needs.render_context.draw_interface': draw_full_interface - filtering out [needs_config_writer.unsupported_type]
WARNING: Unsupported type at 'needs.render_context.draw_module': draw_full_module - filtering out [needs_config_writer.unsupported_type]
WARNING: Unsupported type at 'needs.render_context.draw_component': draw_full_component - filtering out [needs_config_writer.unsupported_type]
WARNING: Unsupported type at 'needs.render_context.draw_feature': draw_full_feature - filtering out [needs_config_writer.unsupported_type]
```

Start by reading issue 288 and tracing the Sphinx configuration paths named in the warnings: needs.render_context.draw_interface, draw_module, draw_component, and draw_feature. Identify where these custom class instances enter the configuration; done means they are no longer stored there and the unsupported-type warnings disappear.

Written by the indexing model from the issue text.