feat: add link formatting to PDF converters

[zcxGGmu]

Summary

• Add link_format to PyPDFToDocument and PDFMinerToDocument with markdown, plain, and none modes.
• Preserve default text-only extraction when link_format="none".
• Add hyperlink PDF fixture coverage for PyPDF, PyPDF layout mode, and PDFMiner.
• Document the new option and add a release note.

Fixes #10677

Testing

• hatch -e test run pytest test/components/converters/test_pypdf_to_document.py test/components/converters/test_pdfminer_to_document.py
• hatch -e test run mypy --python-version 3.13 --install-types --non-interactive --cache-dir=.mypy_cache/ haystack/components/converters/utils.py haystack/components/converters/pypdf.py haystack/components/converters/pdfminer.py
• hatch run fmt-check haystack/components/converters/utils.py haystack/components/converters/pypdf.py haystack/components/converters/pdfminer.py test/components/converters/test_pypdf_to_document.py test/components/converters/test_pdfminer_to_document.py
• git diff --check

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