Support for HPA Behaviour (autosacaling/v2beta2)

[tr-fteixeira]

Initially thought it was a bug, but now seems more like a feature/enhancement.

While testing new HPA functionality introduced in k8s 1.18 on autoscaling/v2beta2, we've noticed that the -primary copies of the resources didn't have the proper spec definition.

Digging a bit further, seems like it is just not there yet..

The proposal is: this would need to be changed to v2 and

Behavior:    hpa.Spec.Behavior,

added here and on a few other places, 2 or 3 at most.

And as we are adding something new, would also need to validate the contents before updates, here.

Let me know if that works or if there are any concerns with the approach..
Thanks =)

[stefanprodan]

My only concern is about Kubernetes version compatibility, Flagger supports Kubernetes >= 1.14. Does autoscaling/v2beta2 work on 1.14, is the Behavior field ignored?

[stefanprodan]

Implemented in #740