Starting blob event trigger fails with 'Resource cannot be updated during provisioning' - now waits for provisioning to complete before retrying #484

[NowinskiK]

private/Start-Trigger.ps1

• Added break after a successful Start-AzDataFactoryV2Trigger call (avoids 4 redundant calls that previously always ran)
• On failure, checks if the error is "cannot be updated during provisioning" — the Azure error returned when a BlobEventsTrigger is still setting up its Event Grid subscription
• If it is, polls Get-AzDataFactoryV2Trigger every 10 seconds (up to 5 minutes) until Properties.ProvisioningState is no longer 'Provisioning', then retries the start
• All other errors keep the existing 2-second retry behaviour

test/Start-Trigger.Tests.ps1

• Updated existing mocks from Write-Error (non-terminating, not caught by catch) to throw (terminating, matches real Azure cmdlet behaviour)
• Added a new test that verifies: provisioning error → polls twice (Provisioning → Succeeded) → retries start successfully