Add support for k3s monitoring

[matofeder]

As a CSP I want to utilize my IaaS management k3s cluster with SCS Observability solution, and observe the k3s cluster itself as well as the IaaS infrastructure around.

[matofeder]

There are at least 3 issues we have to tackle if we want to adapt the current Observability solution to be able to monitor k3s clusters:

1. K3s control plane components kube-scheduler, kube-proxy, and kube-controller do not expose metrics endpoints (by default)
   Those metrics endpoints should be enabled, see Expose kube-scheduler, kube-proxy and kube-controller metrics endpoints k3s-io/k3s#3619 (comment)
   • This configuration should be part of k3s deployment, hence there is nothing to do on the Observability side, just update the docs to inform k3s users to do so
2. kube-prometheus-stack helm values should be adjusted to monitor endpoints outside the k8s overlay network, because the k3s runs as a single process on the host, see see Expose kube-scheduler, kube-proxy and kube-controller metrics endpoints k3s-io/k3s#3619 (comment)
3. K3s is exposing metrics from all CP components in each of them. So we will get duplicated data in the Prometheus. see Expose kube-scheduler, kube-proxy and kube-controller metrics endpoints k3s-io/k3s#3619, try workaround mentioned here [complete stack] Stack is not working by default on K3S clusters, enable it to work out of the box on K3S prometheus-community/helm-charts#2865 (comment)