Leverage Resources for handling documents

[ceberam]

In Docling MCP we leverage an internal cache for handling converted documents.
We should explore whether MCP's resources could provide a better solution.

[vivek12345]

@ceberam I can pick this up too. Just want to understand if you are thinking of replacing the cache with resources or should we
Keep the cache, add Resources as a read interface like for list_cached_documents and get_cached_document