Google generators return answers instead of replies

[anakin87]

Generators in Google integrations return answers instead of replies in the output dictionary.

This makes it difficult to swap them with other Generators.
We should fix this inconsistency.

Tasks

Preview Give feedback

1. The changes are merged in the main branch (Code + Docstrings)
2. The package has been released on PyPI
3. Docs at https://docs.haystack.deepset.ai/ were updated
4. Integration tile on https://github.com/deepset-ai/haystack-integrations was updated (in review)
5. Notebooks on https://github.com/deepset-ai/haystack-cookbook were updated (in review)
6. Tutorials on https://github.com/deepset-ai/haystack-tutorials were updated (if needed)
7. Articles on https://github.com/deepset-ai/haystack-home/tree/main/content were updated (in review)