Add logging field validator CI job for Workhorse

What does this MR do and why?

Adds a new CI job to validate logging fields using LabKit's field validator tool. This helps ensure logging field consistency across the workhorse codebase.

References

gitlab-org/quality/quality-engineering/team-tasks#4110 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Check out the branch malvarez-add-logging-field-validator.
2. Go to the Workhorse directory cd workhorse.
3. Run go get gitlab.com/gitlab-org/labkit/v2/cmd/validate-log-fields.
4. Run go run gitlab.com/gitlab-org/labkit/v2/cmd/validate-log-fields ..
5. Observe Found 9 deprecated logging field offense(s) — all tracked in .labkit_logging_todo.yml. No action required..

In the MR

1. Check the related job workhorse:logging-field-validator and verify it's successful.

MR acceptance checklist

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