We don't calculate k8s resource saturation when no limits are set

Some Kubernetes services have empty saturation charts for kube_container_cpu. Here's the websockets service:

The KAS service is nowhere near saturation, but does have saturation data:

The problem appears to be that kube_container_cpu depends on container_spec_cpu_quota to help calculate the denominator: https://gitlab.com/gitlab-com/runbooks/-/blob/689fb342c49869e089ea05d8accf3330f0bdb64c/metrics-catalog/saturation/kube_container_cpu.libsonnet#L23

But this is only set for services that have a limit at all. KAS does have limits, but websockets doesn't. The websockets service does have a memory limit, and so its memory saturation chart is present.

I noticed this while looking at #963 (closed).