Enable support for docling V2 supported filetypes

[khaledsulayman]

Once #334 and #350 are completed, we'll have migrated to the hierarchical chunker and have a list of filetypes we support defined somewhere in code.

Docling V2 adds support for html, docx, and pptx, so we should theoretically be able to support those on our end by adding them to our supported filetypes.

[khaledsulayman]

this might not be blocked by #350 after all, since the newer docling filetypes should still work with the legacy format that we currently consume.

[github-actions]

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