Remove unused prometheus alerts/metrics finders
What does this MR do and why?
Changes: Removes Projects::Prometheus::AlertsFinder and PrometheusMetricsFinder, both of which are no longer used and the corresponding models/tables are intended for deletion.
Context: This MR cleans up a portion of dead code related to the removal of devopsmonitor Category:Metrics features. The Metrics Dashboard & Prometheus Metrics/Alerts (used for monitoring apps deploying using gitlab) were deprecated in 14.7 and removed from the product in 16.0.
- grouprespond related issue: Metrics: Delete models & database tables/columns (#397142)
- Monitor:Metrics removal epic: Monitor: Metrics Deprecation and Removal (&10107)
- Reference MR with all related removals: Draft: Remove all remaining metrics dashboard-r... (!160325 - closed)
- Metrics removal is blocking cells: Drop old unused tables for prometheus alerts (#461838 - closed)
MR acceptance checklist
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How to set up and validate locally
All related features were disabled in %16.0, and have been partially deleted since then. So there's nothing really to test here. It's no longer possible to set up the features.