expose workflow failure reason to api

[LawyZheng]

[!IMPORTANT] Adds failure_reason to WorkflowRunStatusResponse and updates build_workflow_run_status_response to include it.

• Behavior:
  • Adds failure_reason field to WorkflowRunStatusResponse in workflow.py to expose workflow failure reasons.
  • Updates build_workflow_run_status_response in service.py to include failure_reason from workflow_run.
• Models:
  • Adds failure_reason to WorkflowRunStatusResponse in workflow.py.

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