feat: add Docling reader and node parser

[vagenas]

Description

Docling extracts PDF documents to a rich representation (incl. layout, tables etc.), which it can export to Markdown or JSON.
As outlined in the Docling Technical Report, Docling is based on two models developed by IBM Research, namely a DocLayNet-based layout analysis model and the TableFormer table recognition model.

This PR adds Docling support to LlamaIndex by introducing:

• a Docling Reader (llama_index.readers.docling.DoclingReader, which can export to Markdown and JSON, and
• a Docling Node Parser (llama_index.node_parser.docling.DoclingNodeParser), which can parse the above-mentioned JSON format to LlamaIndex nodes.

By using these extensions, LlamaIndex users will be able to leverage Docling's conversion quality as well as as the rich metadata it can extract — as showcased in the example notebook of this PR.

Dependencies

• docling: Docling PDF conversion
• docling-core: Document document data model and core transformations (e.g. chunking)

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Added new unit/integration tests
• Added new notebook (that tests end-to-end)
• I stared at the code and made sure it makes sense

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
  • ⚠️ added docstrings & an example notebook, but docs deployment within MkDocs remains to be clarified
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran make format; make lint to appease the lint gods

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[vagenas]

Thanks @logan-markewich for the quick reaction! 🙏

Regarding the unit tests, I guess it's still some silly path resolution glitch - or could it be there is something filtering out non-Python / test data files (e.g. JSON) on the fly? 🤔

Besides, Docling supports Python 3.10 and upwards & I see that e.g. the coverage GH Action is hard-coded to 3.9. Perhaps you have some idea how to handle this?

[vagenas]

@logan-markewich
Do you folks take care of updating the docs separately?

Or otherwise can you guide how to best address the two points below?

I would namely also like to include the doc-related changes for:

• docs/mkdocs.yml
• docs/docs/api_reference/node_parser/docling.md
• docs/docs/api_reference/readers/docling.md
• docs/docs/modules_guides/loading/connector/modules.md

However I experienced some discrepancies when building docs locally:

1. (some .md files were causing the build to fail (e.g. docs/docs/api_reference/tools/oracleai.md) so I had to remove them locally for it to work, and
2. calling python docs/prepare_for_build.py to refresh docs/mkdocs.yml also adds other entries, not related to Docling.

[logan-markewich]

@vagenas we take care of docs manually, docs are manually published when a release of llama-index-core / llama-index is made (this is what /stable of the docs points to)

The prepare_for_build script takes care of everything, but I generally only run it before a release (hence it adding stuff unrelated to docling)

This usually happens every 3ish days