make docs great again (#6823)

docs/_static/getting_started/indexing.jpg

docs/_static/getting_started/querying.jpg

docs/_static/getting_started/rag.jpg

docs/_static/storage/storage.png

docs/api_reference/callbacks.rst

docs/api_reference/composability.rst

docs/api_reference/example_notebooks.rst

docs/api_reference/index.rst

docs/api_reference/indices.rst

docs/api_reference/indices/empty.rst

docs/api_reference/indices/kg.rst

docs/api_reference/indices/list.rst

docs/api_reference/indices/struct_store.rst

docs/api_reference/indices/table.rst

docs/api_reference/indices/tree.rst

docs/api_reference/indices/vector_store.rst

docs/api_reference/langchain_integrations/base.rst

docs/api_reference/llm_predictor.rst

docs/api_reference/llms.rst

docs/api_reference/llms/azure_openai.rst