feat(plugin): Introduce plugin support for document conversion

[ayoub-ibm]

This change enables users to extend the document conversion process with custom logic through plugins.

• Introduced a PluginManager to handle preprocessing and postprocessing plugins in DocumentConverter.
• Updated DocumentConverter to accept and initialize a list of plugins.
• Implemented plugin execution within the document processing pipeline, enabling custom modifications before and after conversion.
• Updated ConversionResult to include metadata about the plugins used during conversion.
• Updated the CLI to accept plugin paths and load them dynamically.
• Expanded documentation with examples for creating and using plugins.
• Added test cases to verify plugin integration and ensure correct execution in various scenarios.

Checklist:

• Documentation has been updated.
• Examples have been added.
• Tests have been added.

[mergify]

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[dolfim-ibm]

@ayoub-ibm Thanks for this feature proposal. We are reviewing if the high-level concepts make sense in the overall Docling design. Will keep you posted.

Meanwhile, we noticed your commits are missing the DCO sign-off. Here are some instructions for adding it

To add your Signed-off-by line to every commit in this branch:

Ensure you have a local copy of your branch by checking out the pull request locally via command line.
In your local branch, run: git rebase HEAD~1 --signoff
Force push your changes to overwrite the branch: git push --force-with-lease origin feature/plugin-support

[ayoub-ibm]

@dolfim-ibm Thanks for the feedback.

I've corrected the missing DCO sign-off. My apologies for the oversight.

I'll also be adding more to the "Concepts" section soon to better explain and showcase the plugins implementation.

[mergify]

Merge Protections

Your pull request matches the following merge protections and will not be merged until they are valid.

🟢 Enforce conventional commit

Wonderful, this rule succeeded.

Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?(!)?:

[PeterStaar-IBM]

Closing this PR for now.