Add support for HPA

[npolshakova]

kgateway version

main

Is your feature request related to a problem? Please describe.

The kgateway deployer helm chart can exposes HorizontalPodAutoscaler which is disabled by default.

We should first decide whether we want to keep it there or remove it.

If we want to keep it, there are a few issues that currently prevent it from working:

• We need to add it to the GVKs to watch here (by setting gateway.autoscaling.enabled to true) so that the deployer will watch for changes to any HPA it owns
• Need to add v2 autoscaler to the schemes here
• Need to add autoscaler permissions to the deployer ClusterRole
• Need to add code in merge.go to deep merge autoscaling config