Monitor pv size for Kubernetes-api plugin

Hi, 

This is already possible with the k8s/prometheus plugin: 

/usr/lib/centreon/plugins//centreon_prometheus_api.pl --plugin=cloud::prometheus::restapi::plugin --mode=expression --hostname=<PROMETHEUSAPIIP> --url-path='/api/v1' --port='80' --proto='http'  --query='used,(kubelet_volume_stats_used_bytes{namespace="a-namespace",persistentvolumeclaim="data-galaxion-prod-salt-redis-ha-server-0"} / kubelet_volume_stats_capacity_bytes{namespace="a-namespace",persistentvolumeclaim="data-pvc-name"}) * 100' --instance='persistentvolumeclaim' --output='data-pvc-name is used: %{used}%' --multiple-output='' --warning-status='%{used} > 80' --critical-status='%{used} > 90' --header='Host:fqdn.prod.lan'

But we add this idea to the backlog so we can make it easier to deploy.