Expose transcript completion and failure times consistently

[desicochrane]

Please describe your feature request
When I fetch the transcript, say, when I'm polling, the response does not include the time the transcription finished.

However, the completion time is exposed when I export transcript jobs via CSV.

This makes it troublesome to synchronize data on my side. For my monitoring, it's helpful to have logs for when things started, failed, etc.

Ideally, the CSV export data and response should align so I can better reconcile the job data:

• uploaded timestamp
• transcription job start timestamp
• transcription job completed timestamp
• transcription job failed timestamp

Describe alternatives you've considered
I'm just regularly importing the CSV to capture the missing completion times and doing my best to reconcile.