add kube recording rule for labeling container_spec_cpu_shares metrics
Add kube recording rule for container_spec_cpu_shares:labeled
metrics. This is needed to create saturation metrics based on container shares ("requests" in K8s). We already measure CPU saturation based on container_spec_cpu_quota:labeled
("limits" in K8s), but we don't have set limits for all our containers.
Needed for !3642 (closed).
Related to gitlab-com/gl-infra/delivery#1799 (moved).