* fix: move kube_control_plane reserved vars to correct group_vars location
The file inventory/sample/group_vars/k8s_cluster/kube_control_plane.yml
was being applied to the whole k8s_cluster group instead of only
kube_control_plane. Move it to group_vars/kube_control_plane.yml so the
higher CPU/memory reservations only affect control-plane nodes.
* fix getting-started.md with new kube_control_plane.yml path
