New structured data extraction tutorial, cleanup and crosslinks (#16979)

...docs/examples/structured_outputs/structured_outputs.ipynb

docs/docs/module_guides/querying/structured_outputs/index.md

...le_guides/querying/structured_outputs/pydantic_program.md

docs/docs/understanding/extraction/index.md

docs/docs/understanding/extraction/lower_level.md

docs/docs/understanding/extraction/structured_llms.md

docs/docs/understanding/extraction/structured_prediction.md

docs/docs/use_cases/extraction.md

docs/mkdocs.yml