[Feature] Support OpenSearch VectorDB and Bedrock Knowledge Bases

[cheungdaven]

Support OpenSearch VectorDB and Bedrock Knowledge Bases.

OpenSearch VectorDB: https://opensearch.org/platform/search/vector-database.html
Bedrock Knowledge Bases: https://aws.amazon.com/bedrock/knowledge-bases/

[shreyash2106]

Tutorial for Bedrock KB integration: https://aws.amazon.com/blogs/aws/knowledge-bases-now-delivers-fully-managed-rag-experience-in-amazon-bedrock/