Name queue worker job traces with job class

[whi-tw]

What problem does this pull request solve?

Trello card: https://trello.com/c/KnaPaYVl/3269-tracing-for-cron-jobs-queue-worker

This means that in the trace map, it's easier to understand
where the traces are being emitted from. As there's no user interaction
that triggers these jobs, there's no 'interaction wrapper' around
the traces.

This is related to govuk-forms/forms-deploy#2266

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• Has all relevant documentation been updated?

[github-actions]

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