docs: usage metadata extraction (#460)

apps/docs/docs/modules/data_index.md

apps/docs/docs/modules/data_loader.md

apps/docs/docs/modules/documents_and_nodes/_category_.yml

apps/docs/docs/modules/documents_and_nodes/index.md

...s/docs/modules/documents_and_nodes/metadata_extraction.md

apps/docs/docs/modules/embedding.md

apps/docs/docs/modules/index.md

apps/docs/docs/modules/llm.md

apps/docs/docs/modules/vector_stores/_category_.yml

apps/docs/docs/modules/vector_stores/qdrant.md