skip eviction when pod creation time is below minPodAge threshold setting (#1475)

* skip eviction when pod creation time is below minPodAge threshold setting

In the default initialization phase of the descheduler, add a new
constraint to not evict pods that creation time is below minPodAge
threshold.

Added value:

- Avoid crazy pod movement when the autoscaler scales up and down.

- Avoid evicting pods when they are warming up.

- Decreases the overall cost of eviction as no pod will be evicted
  before doing significant amount of work.

- Guard against scheduling. Descheduling loops in situations where
  the descheduler has a different node fit logic from scheduler,
  like not considering topology spread constraints.

* Use *time.Duration instead of uint for MinPodAge type

* Remove '(in minutes)' from default evictor configuration table

* make fmt

* Add explicit name for Duration field

* Use Duration.String()

pkg/framework/plugins/defaultevictor/zz_generated.deepcopy.go

@@ -41,6 +41,11 @@ func (in *DefaultEvictorArgs) DeepCopyInto(out *DefaultEvictorArgs) {
 		*out = new(api.PriorityThreshold)
 		(*in).DeepCopyInto(*out)
 	}
+	if in.MinPodAge != nil {
+		in, out := &in.MinPodAge, &out.MinPodAge
+		*out = new(v1.Duration)
+		**out = **in
+	}
 	return
 }