feat: add `FilterByNumWords` component

[aicam]

Proposed Changes:

FilterByNumWords is used to filter output of retrievers in a pipeline to make sure it does not exceeds LLM input size. This component is added in preprocessors module and can be used in pipelines. It counts number of words simply by counting .split(' ').

Usage:

    from haystack.document_stores.in_memory import InMemoryDocumentStore
    from haystack.components.retrievers.in_memory import InMemoryBM25Retriever
    from haystack.components.preprocessors.filter_by_num_words import FilterByNumWords

    rag_pipeline = Pipeline()
    rag_pipeline.add_component(instance=InMemoryBM25Retriever(document_store=InMemoryDocumentStore()), name="retriever")
    rag_pipeline.add_component(instance=FilterByNumWords(), name="filter_by_num_words")
    rag_pipeline.connect("retriever", "filter_by_num_words.documents")

How did you test it?

Unit testing added.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[CLAassistant]

All committers have signed the CLA.

[vblagoje]

@aicam thanks for this contribution. I agree with you this is something that many users might need but due to its simplicity I'm not sure we should include it as the main component as most users can implement, and further customize, such a component themselves.

cc @julian-risch @shadeMe

[aicam]

@aicam thanks for this contribution. I agree with you this is something that many users might need but due to its simplicity I'm not sure we should include it as the main component as most users can implement, and further customize, such a component themselves.

cc @julian-risch @shadeMe

Thank you for your feedback. I understand the concern regarding the simplicity of the component. I'd be happy to work on making the component more customizable, allowing users to tailor it to their specific needs. Would this make it more suitable for inclusion as a main component? I’m open to suggestions on how to enhance its flexibility and usefulness for the broader user base.

[vblagoje]

@aicam thanks for your effort and eagerness to contribute – it’s always great to see enthusiasm from our community! However, after internal discussion, we believe it might not be the best fit as a main component due to its simplicity which most users can implement and customize themselves.

Having said that we’d welcome your skills applied in other tasks. If you’re interested feel free to take a look at our Contributions wanted list where you might find other issue that pique your interest. If in doubt reach out to me or another core developer cc @julian-risch . Looking forward to your future contributions!