Add support for model.meta

Currently as stated in the docs of this package, the “meta” key from the “nodes” toplevel node isn’t supported.

Can this be added please? It is very useful to have access to “meta” on node/model level.

In order to do this, probably adding this should be enough to this file https://github.com/cube-js/cube_dbt/blob/main/src/cube_dbt/model.py

@property
def meta(self) -> dict:
return self._model_dict.get('meta', {})