Log backup & restore duration in telemetry

**Is your feature request related to a problem? Please describe.**
We don't have an understanding of how long backup & restore take to run on customer environments.

**Describe the solution you'd like**
I would like to see a new "duration" field captured in log-based telemetry, at the end of a backup & restore operation.

**Describe alternatives you've considered**
None

**Additional context**
N/A

Jira issue: CRDB-25094

Start by locating the backup and restore operation entry points and the log-based telemetry emitted when each completes. Add a duration field to the telemetry at the end of both operations, and verify that backup and restore logs report how long they took.

Written by the indexing model from the issue text.