Add second Azure Key Vault secret URL

[mrm9084]

Fixing build pipeline issue https://dev.azure.com/azure-sdk/internal/internal%20Team/_build/results?buildId=5533870&view=logs&j=047d1ede-b9d4-5728-2d64-16f68eb8c477&t=8b07845f-1009-5443-c9a8-8968c41005a1&l=9689

Description

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[Copilot]

Pull Request Overview

This PR adds a second Key Vault secret URL to the App Configuration test resources template. The change enables testing scenarios that require multiple Key Vault secret references.

• Adds azureKeyVaultSecretUrl2 variable pointing to a second test secret
• Exposes the new secret URL via APPCONFIGURATION_KEYVAULT_SECRET_URL2 output