Removes read_prometheus_alert permission in favor of admin_operations

What does this MR do and why?

Changes: Removes the :read_prometheus_alerts permission as prometheus alerts are being removed. The :admin_operations permission is the more correct permission for the remaining usages.

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 - closed)
• 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)

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.rubocop_todo/gitlab/bounded_contexts.yml

@@ -1379,7 +1379,6 @@ Gitlab/BoundedContexts:
     - 'app/policies/project_policy.rb'
     - 'app/policies/project_snippet_policy.rb'
     - 'app/policies/project_statistics_policy.rb'
-    - 'app/policies/prometheus_alert_policy.rb'
     - 'app/policies/protected_branch_access_policy.rb'
     - 'app/policies/protected_branch_policy.rb'
     - 'app/policies/release_policy.rb'