docs: add an example of RAG with OpenSearch (#2238)

* docs: add an example of RAG with OpeanSearch

Signed-off-by: Cesar Berrospi Ramis <[email protected]>

* chore: pin latest docling-core and update uv.lock

Pin latest version release of docling-core in pyproject.toml
Update the dependencies in uv.lock file
Run the notebook rag_opensearch.ipynb to pick up changes from docling-core

Signed-off-by: Cesar Berrospi Ramis <[email protected]>

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Signed-off-by: Cesar Berrospi Ramis <[email protected]>

Author: ceberam