Fix type errors, pass collection id

[NolanTrem]

[!IMPORTANT] Fix type errors and improve type hinting, ensuring correct collection ID passing in various functions.

• Type Hinting Improvements:
  • Replace Union with | for type hinting in agent.py and ingestion_router.py.
  • Update type hints in retrieval_service.py and kg_service.py to use modern syntax.
• Parameter Passing:
  • Ensure collection_ids are passed correctly in assign_document_to_collection_relational() in database.py.
  • Pass collection_ids in create_document() in documents_router.py.
• Miscellaneous:
  • Add # type: ignore comments to suppress type errors in various files like ingestion_router.py and management_router.py.
  • Remove duplicate DocumentSearchResult class in responses.py.

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