Add troubleshooting guidance for Azure DevOps pipeline "azd init" errors

[Copilot]

This PR addresses a common issue where users encounter "ERROR: no project exists; to create a new project, run azd init" when deploying .NET Aspire projects via Azure DevOps pipelines.

Problem

Users following the Azure DevOps deployment documentation experience pipeline failures during the provisioning step because azd init generates files (azure.yaml and .azure folder) that are typically not committed to repositories. When pipelines run in clean environments, these files don't exist, causing azd commands to fail.

Solution

Added comprehensive troubleshooting documentation that provides:

1. Root cause explanation - Why the error occurs in CI/CD environments
2. Recommended solution - Running azd init in the pipeline with proper flags:

   - task: AzureCLI@2
     displayName: 'Initialize Azure Developer CLI'
     inputs:
       azureSubscription: '$(AZURE_SERVICE_CONNECTION)'
       scriptType: 'bash'
       scriptLocation: 'inlineScript'
       inlineScript: |
         azd init --from-code --no-prompt
         azd env new $(AZURE_ENV_NAME) --location $(AZURE_LOCATION) --subscription $(AZURE_SUBSCRIPTION_ID)

3. Alternative approaches - Committing files to repository or using proper pipeline configuration
4. Additional troubleshooting - Verification steps for common configuration issues

Changes Made

• Added "Troubleshoot Azure DevOps pipeline deployment" section to aca-deployment-github-actions.md
• Added proactive warning in pipeline configuration section with cross-reference to troubleshooting
• Provided specific guidance for handling unexpected prompts and explained --from-code flag usage
• Included security considerations for committing .azure folder contents

All changes follow the Microsoft Writing Style Guide and pass markdown linting.

Fixes #983.

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Internal previews

📄 File	🔗 Preview link
docs/deployment/azure/aca-deployment-github-actions.md	docs/deployment/azure/aca-deployment-github-actions