Support Firestore as LlamaIndex Storage (#7305)

.vscode/settings.json

CHANGELOG.md

docs/core_modules/data_modules/storage/docstores.md

docs/examples/docstore/FirestoreDemo.ipynb

llama_index/storage/docstore/__init__.py

llama_index/storage/docstore/firestore_docstore.py

llama_index/storage/index_store/__init__.py

llama_index/storage/index_store/firestore_indexstore.py

llama_index/storage/kvstore/__init__.py

llama_index/storage/kvstore/firestore_kvstore.py

tests/storage/conftest.py

tests/storage/docstore/test_firestore_docstore.py

tests/storage/index_store/test_firestore_indexstore.py

tests/storage/kvstore/test_firestore_kvstore.py