Feedback: Backup and Restore Monitoring - document backup and restore logging

Page: https://cockroachlabs.com/docs/v25.2/backup-and-restore-monitoring.html

## What is the reason for your feedback?

[X] Missing the information I need

[ ] Too complicated

[ ] Out of date

[ ] Something is broken

[ ] Other

## Additional details

This page talks about Prometheus metrics. It would be helpful if it also covered

- Where backup/restore logs are writen (e.g. which logging channel)
- What are useful log messages to monitor

Jira issue: DOC-14401