Add constructs for KnowledgeBase and Guardrails

[divekarshubham]

Issue #, if available:

Description of changes: Combining changes from previous pull requests:

• KB: https://github.com/aws-samples/agents-for-amazaon-bedrock-blueprints/pull/4
• Guardrails: https://github.com/aws-samples/agents-for-amazaon-bedrock-blueprints/pull/5

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