Summary

• Adds a new logic-app-slack-alert Terraform module that deploys an Azure Logic App to receive Azure Monitor alert webhook payloads (common alert schema) and forward them to Slack as formatted Block Kit messages
• Message includes alert rule name, severity, status, fired time, affected resource, description, and a deep link (App Insights Failures blade for App Insights alerts, resource overview for all others)
• Slack webhook URL is stored as a SecureString workflow parameter so it does not appear in run history or trigger inputs in the Azure portal
• Exposes trigger_callback_url (sensitive) for registration with an Azure Monitor action group webhook receiver
• Updates virtual-desktop/tfdocs.md to document the principal_id variable and azurerm_role_assignment.avd_autoscale_hostpool

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

Sensitive Information Declaration

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.