Alerting: Add setting to distribute rule group evaluations over time (#80766)

* Simple, per-base-interval jitter

* Add log just for test purposes

* Add strategy approach, allow choosing between group or rule

* Add flag to jitter rules

* Add second toggle for jittering within a group

* Wire up toggles to strategy

* Slightly improve comment ordering

* Add tests for offset generation

* Rename JitterStrategyFrom

* Improve debug log message

* Use grafana SDK labels rather than prometheus labels

packages/grafana-data/src/types/featureToggles.gen.ts

@@ -176,4 +176,6 @@ export interface FeatureToggles {
   cloudRBACRoles?: boolean;
   alertingQueryOptimization?: boolean;
   newFolderPicker?: boolean;
+  jitterAlertRules?: boolean;
+  jitterAlertRulesWithinGroups?: boolean;
 }