Support reranker for Amazon Knowledge Base

[jithinch]

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Feature request

Amazon Knowledge Base now supports rerank API.

When using AWS Knowledge bases, you can provide reranking configuration to improve relevancy of your results. This functionality should be added to Langchain, since it supports the bedrock:Retrieve function.

Motivation

Currently, langchain supports retrieving documents through Amazon Knowledge base but does not support the reranker configuration. Adding support for this will prevent having to use AWS SDK for this functionality.

Proposal (If applicable)

No response