docs: restructure, add API references (#1196)

apps/docs/docs/modules/agent/_category_.yml

apps/docs/docs/modules/chat_engine.md

apps/docs/docs/modules/data_index.md

apps/docs/docs/modules/data_loaders/index.mdx

apps/docs/docs/modules/data_stores/_category_.yml

.../docs/docs/modules/data_stores/chat_stores/_category_.yml

apps/docs/docs/modules/data_stores/chat_stores/index.md

apps/docs/docs/modules/data_stores/doc_stores/_category_.yml

apps/docs/docs/modules/data_stores/doc_stores/index.md

apps/docs/docs/modules/data_stores/index.md

...docs/docs/modules/data_stores/index_stores/_category_.yml

apps/docs/docs/modules/data_stores/index_stores/index.md

apps/docs/docs/modules/data_stores/kv_stores/_category_.yml

apps/docs/docs/modules/data_stores/kv_stores/index.md

...ocs/docs/modules/data_stores/vector_stores/_category_.yml

apps/docs/docs/modules/data_stores/vector_stores/index.md

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

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

apps/docs/docs/modules/embeddings/_category_.yml

...s/modules/embeddings/available_embeddings/mixedbreadai.md