New Serverless Pattern - Add Lambda Durable Functions - Human Approval Pattern

[agawanea]

Issue #, if available: https://github.com/aws-samples/serverless-patterns/issues/2875

Description of changes: This PR adds a new serverless pattern: Lambda Durable Functions - Human-in-the-Loop Approval Pattern

This pattern demonstrates a cost-effective human approval workflow using AWS Lambda Durable Functions. The workflow pauses execution for up to 24 hours while waiting for human approval via email, without incurring compute charges during the wait period.

Testing: Pattern has been fully tested and deployed in us-east-2 region with successful validation of:

• 24-hour timeout handling
• Email notifications with working approve/reject links
• DynamoDB TTL cleanup after expiration
• HTML response pages with proper UTF-8 encoding
• Callback resumption using boto3 send_durable_execution_callback_success API

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