Advanced AI Prompt for CloudWatch Alarm Notification Templating

Act as a ChatOps Integration Engineer. Design an intelligent routing system to transform chaotic, raw JSON CloudWatch Alarm payloads into highly readable, actionable Slack notifications for the engineering team. Architect an AWS Lambda function that intercepts payloads from the [SNS_TOPIC_ARN]. The Python script must parse the deep alarm event data, extract the exact metric failure, and format a beautiful Slack 'Block Kit' message. The message must visibly inject the [SEVERITY_LEVEL] (e.g., P1 - CRITICAL), include deep-links directly back to the specific AWS resource, and append the [CUSTOM_MESSAGE_ATTRIBUTES] (e.g., Runbook URLs, On-Call Roster). Provide the complete Python Lambda code, the required IAM execution role policy, and the step-by-step setup instructions for securely handling the Slack Webhook URL via AWS Secrets Manager.