FAISS in OpenSearch: Support IVF

[tstadel]

As a user I want to use FAISS's IVF index with OpenSearchDocumentStore.

According to https://opensearch.org/docs/latest/search-plugins/knn/knn-index/ FAISS plug-in supports IVF. There are two params nlist and nprobes. As we're not sure whether this is useful, we only support the default values for now and omit configuration of these params. They could be configured via custom_mapping anyway.

• [ ] add ivf option to index_type constructor param
• [ ] set mapping: use default values
• [ ] support product quantization