optional custom index settings in vectorstore

[giacbrd]

Hi, I have simply added a parameter to the ElasticsearchStore class in order to set default settings at index creation, that is made by the VectorStore helper in the Elasticsearch library. It is just arguments traversing calls, there is not much to test. There is also another minor fix in the doctring.

The main benefit of this parameter is to pre-configure the index when using the Elasticsearch vector store, which implicitly creates an index when first documents are added. One can, for example, set a correct number of replicas for his cluster, so that he has not to change it manually after creation, with all the waste of computational effort this implies

[giacbrd]

@miguelgrinberg I had a minor problem: unasync is not a dependency in pyproject.toml, nor is isort. Is this regular?

[miguelgrinberg]

@giacbrd Yes, that is a problem, looks like I missed adding those as dev dependencies in the project files. Thanks.