Add database timings to Sidekiq JSON logs

What does this MR do?

Sidekiq JSON logs have total duration, queuing time, Gitaly time, and CPU time. They don't (before this change) have database time.

We provide two fields: db_duration and db_duration_s. That's because the units between the different duration fields are currently confusing, so providing an explicit unit moves us closer to that goal, while keeping the raw figure in the un-suffixed fields.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.