move all indexes into indices folder

CONTRIBUTING.md

package.json

packages/core/src/Retriever.ts

packages/core/src/index.ts

packages/core/src/indices/BaseIndex.ts

packages/core/src/indices/index.ts

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

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

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

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

...ages/core/src/indices/vectorStore/VectorIndexRetriever.ts

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

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

packages/core/src/tests/CallbackManager.test.ts