[Document Upload Failure Mailer] Launch and Post-release Monitoring

[NB28VT]

After we release the Form526DocumentUploadFailureEmail job in production, we will want to monitor its frequency and catch any errors or exhuastations. I propose this entails:

• (First week), Nathan maintains a close watch on Slack of the two alerts created for this job, exhaustion (the job retried until it gave up) and catastrophic failure (syntax error, not successfully handled by a retry)
• (After first week), Nathan continues to maintain a watch on the alerts
• (Daily) Nathan keeps an eye on the Production Dashboard, which will show when these mailers are getting sent out and what the obscured filename is. If any of the filenames appear to be problematic, Nathan will flag them for the team and investigate.

Turn on form526_send_document_upload_failure_notification flipper in prod

[NB28VT]

This is failing in production, potentially because of some issues with the VA Notify configuration. Realizing now that I'm not logging the actual error message as is done here in the mailer job. Going to submit a PR to do just that so I can capture these errors and debug.