Require ARM endpoint for Azure Stack login validation

[Copilot]

Azure Stack logins were allowed without providing the ARM endpoint, contradicting expected validation from the referenced change.

• Validation

  • LoginConfig.validate now rejects environment=azurestack when resourceManagerEndpointUrl is missing.
  • New action input resource-manager-endpoint surfaces the required ARM endpoint for Azure Stack scenarios.

• Documentation

  • README input table documents resource-manager-endpoint.

• Tests

  • Added coverage ensuring Azure Stack requires resource-manager-endpoint; adjusted existing identity test to supply it.

Example:

- uses: Azure/login@v2
  with:
    environment: azurestack
    resource-manager-endpoint: https://management.azurestack.example.com
    auth-type: SERVICE_PRINCIPAL
    client-id: ${{ secrets.CLIENT_ID }}
    tenant-id: ${{ secrets.TENANT_ID }}
    subscription-id: ${{ secrets.SUBSCRIPTION_ID }}

Original prompt

Reference: f3ea448

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[github-actions]

This PR is idle because it has been open for 14 days with no activity.

[github-actions]

This PR is idle because it has been open for 14 days with no activity.