Correcting OpenSearchVectorStore documentation for AsyncClient import problem (#252)

when AsyncOpenSearch cannot be imported, you need to make sure to
install opensearch-py[async] as documented
[here](https://github.com/opensearch-project/opensearch-py/blob/main/guides/async.md#setup).

This missing detail probably didn't arise yet, as frequently aiohttp is
installed with some other packages, which effectively solved this
problem silently (see
[here](opensearch-project/opensearch-py#332))
but its better we install it exactly as planned by
opensearchpy-maintainers.

Open Question: are dependencies for the community-package not managed
somewhere centrally? If so, opensearch-py[async] should be added there.

Co-authored-by: Georg Wind <[email protected]>
Co-authored-by: Mason Daugherty <[email protected]>

Author: 3 people

libs/community/langchain_community/vectorstores/opensearch_vector_search.py

@@ -17,7 +17,7 @@
 )
 IMPORT_ASYNC_OPENSEARCH_PY_ERROR = """
 Could not import AsyncOpenSearch.
-Please install it with `pip install opensearch-py`."""
+Please install it with `pip install opensearch-py[async]`."""
 
 SCRIPT_SCORING_SEARCH = "script_scoring"
 PAINLESS_SCRIPTING_SEARCH = "painless_scripting"