As a cluster operator using NGF
I want NGF to work with a HorizontalPodAutoscaler
So that I can automate the scaling of my data planes to save on resources and scale up when traffic increases.

NIC PR: nginx/kubernetes-ingress#3276

Acceptance

• The user can setup a HorizontalPodAutoscaler for an NGINX deployment (data plane).
• The user can setup a HorizontalPodAutoscaler for the NGF control plane.
• Update the scaling doc to talk about how to use the HorizontalPodAutoscaler.