Allow query embeddings to be searched for in vectorstore

[rishabh208gupta]

Checked

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Feature request

As part of elastic/elasticsearch-py#2620, we wanted to have the ability to do an mmr search just using the vector embeddings instead of a text query. It would be nice to make query as optional and also allow a vector embedding as an optional param to https://github.com/langchain-ai/langchain/blob/b28bc252c4e7058951c9d3be8ee81595029eab83/libs/core/langchain_core/vectorstores/base.py#L679C9-L679C38

Motivation

To have the flexibility to perform a max_marginal_relevance search using either a text query or a query vector

Proposal (If applicable)

No response