Multiple fixes to make various API reference docs visible to Algolia (#9065)

docs/Makefile

docs/api_reference/index.rst

docs/api_reference/node.rst

docs/api_reference/readers.rst

docs/api_reference/service_context/node_parser.rst

docs/api_reference/storage/vector_store.rst

docs/conf.py

docs/requirements.txt

llama_index/vector_stores/__init__.py