Wrong source configuration class

Hello!

I have different sources types in my Airbyte
When getting them using `sources.list_sources` or `sources.get_source` all configurations are encapsulating in `SourceAirtable` class

Example here printing a source, you can see source_type is postgres, but configuration is wrong, I expect `SourcePostgres`

```
SourceResponse(configuration=SourceAirtable(credentials=None, SOURCE_TYPE=), name='my postgres', source_id='XXX', source_type='postgres', workspace_id='YYY')
```

NB: the API returns correct configuration data