fix persistance, update fromDocuments

apps/docs/docs/end_to_end.md

examples/chatEngine.ts

examples/listIndex.ts

examples/persist.ts

examples/storageContext.ts

examples/vectorIndexCustomize.ts

packages/core/src/dataStructs.ts

packages/core/src/indices/BaseIndex.ts

packages/core/src/indices/list/ListIndex.ts

packages/core/src/indices/vectorStore/VectorStoreIndex.ts

packages/core/src/storage/indexStore/KVIndexStore.ts