Update 2_kb_to_vectordb_opensearch.ipynb

[Christian-kam]

The default CloudFormation stack name is actually "llm-apps-blog-rag" . Struggle to figure this out for about 2 hours. So making the changes to make it easier for others

Issue #, if available: The default CloudFormation stack name is actually llm-apps-blog-rag . Struggle to figure this out for about 2 hours. So making the changes to make it easier for others

Description of changes: Changed the CloudFormation template name is the notebook "2_kb_to_vectordb_opensearch" from "rag22" to "llm-apps-blog-rag"

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