community: Fix Bug in Azure Search Vectorstore search asyncronously

[thedavgar]

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Description:
This PR fixes a bug described in the issue in #24064, when using the AzureSearch Vectorstore with the asyncronous methods to do search which is also the method used for the retriever. The proposed change includes just change the access of the embedding as optional because is it not used anywhere to retrieve documents. Actually, the syncronous methods of retrieval do not use the embedding neither.

With this PR the code given by the user in the issue works.

vectorstore = AzureSearch(
    azure_search_endpoint=os.getenv("AI_SEARCH_ENDPOINT_SECRET"),
    azure_search_key=os.getenv("AI_SEARCH_API_KEY"),
    index_name=os.getenv("AI_SEARCH_INDEX_NAME_SECRET"),
    fields=fields,
    embedding_function=encoder,
)

retriever = vectorstore.as_retriever(search_type="hybrid", k=2)

await vectorstore.avector_search("what is the capital of France")
await retriever.ainvoke("what is the capital of France")

Issue:
The Azure Search Vectorstore is not working when searching for documents with asyncronous methods, as described in issue #24064

Dependencies:
There are no extra dependencies required for this change.

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Name	Status	Preview	Comments	Updated (UTC)
langchain	⬜️ Ignored (Inspect)	Visit Preview		Jul 11, 2024 8:57pm

[chrislrobert]

@thedavgar @efriis @isahers1, this PR caused the regression in issue #24740. I agree that it seems to have fixed the exception that motivated the change, but it also pulled async results handling outside the with block, which caused a new exception. See #24740 for details.