Traffic absent alerts causing pager noise
## Summary
We're getting a lot of pages for sparse metrics (metrics that are intermittently reported). When they go missing, we get alerted because traffic seems to be "absent" - but there was never any traffic in the first place.
I suspect it has something to do with how we're using `offset 1h` or `unless` on our alerting rules.
## Related Incident(s)
* https://gitlab.com/gitlab-com/gl-infra/production/-/issues/8520
* https://gitlab.com/gitlab-com/gl-infra/production/-/issues/8507
## Desired Outcome/Acceptance Criteria
We are no longer getting `*TrafficAbsent` alerts for things that had no traffic to begin with.
## Associated Services
<!--
Apply the appropriate services associated with this corrective action if applicable.
-->
## Corrective Action Issue Checklist
* [x] Link the incident(s) this corrective action arose out of
* [x] Give context for what problem this corrective action is trying to prevent from re-occurring
* [x] Assign a severity label (this is the highest sev of related incidents, defaults to 'severity::4')
* [x] Assign a priority (this will default to 'Reliability::P4')
issue