feat: emit created_at on workflow_run_jobs

[malhussan]

The GitHub API returns created_at on every workflow job, but the stream schema does not declare it, so the SDK drops it before it reaches the target.

This adds the property. Nothing else changes.

created_at is the time the job was queued. started_at is the time a runner picked it up.

Checked against one job, where the API returned created_at at 06:53:03 and started_at at 06:56:24.

Two notes:

• This branches off feature/fix-actions-streams rather than main, because that branch carries the three workflow-stream fixes that are not on main: incremental loading for workflow_runs, the lookback window, and dropping state partitions for workflow_run_jobs. Basing this on main would mean losing those three when the pin moves.
• Rows that are already loaded keep a null created_at. Only new syncs carry it, so a full re-sync is needed for history.

[JohannesRudolph]

lgtm. probably the easiest way to get this in. I wonder however if we should also update the tap to its remote upstream - surely a lot has changed. OTOH - if it works it works, no point in rocking the boat