1. Proposed title of this feature request

HPAScaleToZero feature gate

2. What is the nature and description of the request?

Customer would like to set the minimum replicas in their HorizontalPodAutoscaler to 0. According to this doc it should be possible: https://docs.openshift.com/container-platform/4.10/rest_api/autoscale_apis/horizontalpodautoscaler-autoscaling-v1.html#spec
"minReplicas is the lower limit for the number of replicas to which the autoscaler can scale down. It defaults to 1 pod. minReplicas is allowed to be 0 if the alpha feature gate HPAScaleToZero is enabled and at least one Object or External metric is configured. Scaling is active as long as at least one metric value is available."

However, actually trying to enable this doesn't work:

~~~
$ oc patch FeatureGate/cluster --type=merge -p "{\"spec\":{\"featureSet\":\"HPAScaleToZero\"}}"
The FeatureGate "cluster" is invalid: spec.featureSet: Unsupported value: "HPAScaleToZero": supported values: "", "CustomNoUpgrade", "IPv6DualStackNoUpgrade", "LatencySensitive", "TechPreviewNoUpgrade"
~~~

3. Why does the customer need this? (List the business requirements here)

No immediate impact but customer would like to scale down certain applications to 0 when not in use.