feat: Add Cohere ranker

[AnushreeBannadabhavi]

Related Issues

• part of CohereRanker #645

Proposed Changes:

Add CohereRanker for Haystack 2.0.
Performs reranking of documents using Cohere reranking models. Reranks retrieved documents based on semantic relevance to a query.
For more information refer to Cohere reranker

How did you test it?

• Tests have been added in test_cohere.py
• Tested the example: cohere_ranker_in_a_pipeline.py

[CLAassistant]

All committers have signed the CLA.

[anakin87]

Very good work. Thanks! 💙

• I found some small opportunities for improvement (see the comments).

• for security reasons, the integration tests that require an API key do not run on community PRs. Have you had the chance to try your component locally?

• I also (moved and) update the corresponding issue (CohereRanker #645) to keep track of all the work needed (by you and us) to declare this feature ready.

[AnushreeBannadabhavi]

Hi @anakin87! Thank you for your feedback! :)
I agree with all your comments and suggestions and I've implemented them.

To your second point, yes I've tried the component locally. I ran integration tests by setting the COHERE_API_KEY environment variable and also tested with the example in cohere_ranker_in_a_pipeline.py. Let me know if any additional testing is required and I can do that too.

[anakin87]

Excellent work!

I have tried the component and works as expected.