ollama: mount integration under haystack_integrations.*

[masci]

No description provided.

[anakin87]

Checklist

• Update the structure, the code, and examples on haystack-core-integrations
• release a new version of the package
• Update the integration tile on https://github.com/deepset-ai/haystack-integrations
• Update the docs at https://docs.haystack.deepset.ai/
• Update the notebooks on https://github.com/deepset-ai/haystack-cookbook (if needed)