Add RAGAS evaluation framework integration

[julian-risch]

Summary and motivation

Integrate the RAGAS evaluation framework by implementing a new RAGASEvaluator component

Detailed design

Based on the proposal deepset-ai/haystack#6784 we need to implement an RAGASEvaluator component that is initialized with one metric and an OpenAI API key. Depending on the particular metric, the component expects for example question, answer and context as input and outputs a dictionary with the calculated score.

Checklist

If the request is accepted, ensure the following checklist is complete before closing this issue.

• The code is documented with docstrings and was merged in the main branch
• Docs are published at https://docs.haystack.deepset.ai/
• There is a Github workflow running the tests for the integration nightly and at every PR
• A label named like integration:<your integration name> has been added to this repo
• The labeler.yml file has been updated
• The package has been released on PyPI
• An integration tile has been added to https://github.com/deepset-ai/haystack-integrations: Add integration tile for Ragas haystack-integrations#168
• The integration has been listed in the Inventory section of this repo README
• There is an example available to demonstrate the feature
• The feature was announced through social media

[julian-risch]

With the social media announcement, this issue is closed now: https://twitter.com/Haystack_AI/status/1760726816526925839