Demote HPA tests from release-blocking

Add a Feature:HPA tag to these tests so they're not picked up by
the release-blocking job that focuses on [Serial] tests (but
excludes [Feature:.*] tests)

They take a combined 70 minutes on average. If they really need
to be in release-blocking as implemented, we should consider a
separate job to focus just on this feature.

test/e2e/autoscaling/horizontal_pod_autoscaling.go

@@ -28,7 +28,7 @@ import (
 
 // These tests don't seem to be running properly in parallel: issue: #20338.
 //
-var _ = SIGDescribe("[HPA] Horizontal pod autoscaling (scale resource: CPU)", func() {
+var _ = SIGDescribe("[Feature:HPA] Horizontal pod autoscaling (scale resource: CPU)", func() {
 	var rc *common.ResourceConsumer
 	f := framework.NewDefaultFramework("horizontal-pod-autoscaling")