Add trigger metadata columns to duo_workflows_workflows

What does this MR do and why?

This MR partly addresses: #605895 (closed)

It adds trigger metadata columns (trigger_source and trigger_flow_trigger_id) to duo_workflows_workflows table to support autonomous service account execution of Duo workflows without composite identity.

The migrations set up the remaining work in #605895 (closed).

Why

Downstream systems should have a way to distinguish autonomous SA-initiated runs from human-triggered runs. These columns provide attribution metadata set at workflow creation time, ensuring the trigger source, acting SA, and flow trigger config are traceable throughout the workflow lifecycle. In particular, trigger_source is immutable, guaranteeing a run's origin can't be altered after creation.

Their addition captures who/what triggered a workflow, thus, helping to satisfy requirement 7 (Persist trigger source and actor metadata to capture trail of who/what triggered a workflow) of the implementation design.

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