docs: restructure, add API references (#1196)

apps/docs/docs/modules/embeddings/index.md

apps/docs/docs/modules/evaluation/_category_.yml

apps/docs/docs/modules/ingestion_pipeline/_category_.yml

apps/docs/docs/modules/llms/_category_.yml

apps/docs/docs/modules/llms/available_llms/fireworks.md

apps/docs/docs/modules/llms/index.md

apps/docs/docs/modules/node_parser.md

apps/docs/docs/modules/node_postprocessors/index.md

...ocs/modules/node_postprocessors/mixedbreadiai_reranker.md

apps/docs/docs/modules/prompt/_category_.yml

apps/docs/docs/modules/prompt/index.md

apps/docs/docs/modules/query_engines/_category_.yml

apps/docs/docs/modules/response_synthesizer.md

apps/docs/docs/modules/retriever.md