Added langfuse dependency to the requierements.txt file.

[Michelklingler]

Pull Request Checklist

• [ X ] Description: Briefly describe the changes in this pull request.
• [ X ] Changelog: Ensure a changelog entry following the format of Keep a Changelog is added at the bottom of the PR description.
• [ X ] Documentation: Have you updated relevant documentation?
• [ X ] Dependencies: Are there any new dependencies? Have you updated the dependency versions in the documentation?

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Description

Added Langfuse dependency to the requirements.txt file.
This will enable monitoring capabilities via LiteLLM middleware.

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Changelog Entry

Added

• Added Langfuse dependency to requierement.txt