Enhanced backup log messages

[data-matt]

Is your feature request related to a problem? Please describe. We need to be able to send backup events downstream, another team consumes our logging telemetry and needs the following details about a backup

• Backup started
• Backup finished
• Backup failure
• Backup failure reason
• Backup status
• Backup size
• Backup destination (S3 etc)
• Backup duration

Describe the solution you'd like Emit the above as messages in the log.

Additional context We've looked at the eventlog and that doesn't work for us.

Jira issue: CRDB-35695

[blathers-crl[bot]]

cc @cockroachdb/disaster-recovery