Experimental support for ScheduledOverrides (#515)

This adds the initial version of ScheduledOverrides to HorizontalRunnerAutoscaler.
`MinReplicas` overriding should just work.
When there are two or more ScheduledOverrides, the earliest one that matched is activated. Each ScheduledOverride can be recurring or one-time. If you have two or more ScheduledOverrides, only one of them should be one-time. And the one-time override should be the earliest item in the list to make sense.

Tests will be added in another commit. Logging improvements and additional observability in HRA.Status will also be added in yet another commits.

Ref #484

controllers/horizontalrunnerautoscaler_controller.go

@@ -185,12 +185,52 @@ func (r *HorizontalRunnerAutoscalerReconciler) SetupWithManager(mgr ctrl.Manager
 		Complete(r)
 }
 
+func (r *HorizontalRunnerAutoscalerReconciler) matchScheduledOverrides(log logr.Logger, now time.Time, hra v1alpha1.HorizontalRunnerAutoscaler) (*int, *Period, *Period, error) {
+	var minReplicas *int
+	var active, upcoming *Period
+
+	for _, o := range hra.Spec.ScheduledOverrides {
+		a, u, err := MatchSchedule(
+			now, o.StartTime.Time, o.EndTime.Time,
+			RecurrenceRule{
+				Frequency: o.RecurrenceRule.Frequency,
+				UntilTime: o.RecurrenceRule.UntilTime.Time,
+			},
+		)
+		if err != nil {
+			return minReplicas, nil, nil, err
+		}
+
+		// Use the first when there are two or more active scheduled overrides,
+		// as the spec defines that the earlier scheduled override is prioritized higher than later ones.
+		if active == nil {
+			active = a
+
+			if o.MinReplicas != nil {
+				minReplicas = o.MinReplicas
+			}
+		}
+
+		if upcoming == nil || (u != nil && u.StartTime.Before(upcoming.StartTime)) {
+			upcoming = u
+		}
+	}
+
+	return minReplicas, active, upcoming, nil
+}
+
 func (r *HorizontalRunnerAutoscalerReconciler) computeReplicasWithCache(log logr.Logger, now time.Time, rd v1alpha1.RunnerDeployment, hra v1alpha1.HorizontalRunnerAutoscaler) (int, int, *int, error) {
 	minReplicas := defaultReplicas
 	if hra.Spec.MinReplicas != nil && *hra.Spec.MinReplicas >= 0 {
 		minReplicas = *hra.Spec.MinReplicas
 	}
 
+	if m, _, _, err := r.matchScheduledOverrides(log, now, hra); err != nil {
+		return 0, 0, nil, err
+	} else if m != nil {
+		minReplicas = *m
+	}
+
 	var suggestedReplicas int
 
 	suggestedReplicasFromCache := r.fetchSuggestedReplicasFromCache(hra)