Support for Metrics

[flofourcade]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind feature

What happened:

The vSphere CSI driver currently doesn't support exposing vSphere volume metrics (capacity, usage, ...) via the GetNodeVolumeStats endpoints.
The GetNodeVolumeStats endpoint is used by kubelets to expose kubelet_stats_volume* prometheus metrics.

What you expected to happen:

The CSI driver should implement this feature.
These metrics could then be used by monitoring / alerting stacks

How to reproduce it (as minimally and precisely as possible):
By using prometheus, or directly getting kubelet prometheus endpoint with curl.
No kubelet_stats_volume* are exposed for vSphere volumes

Anything else we need to know?:

Environment:

• csi-vsphere version: 1.0.1
• vsphere-cloud-controller-manager version: 1.0.0
• Kubernetes version: 1.16.1
• vSphere version: 6.7U3
• OS (e.g. from /etc/os-release): CentOS 7
• Kernel (e.g. uname -a):
• Install tools: Kubeadm
• Others:

[yuyiying]

/assign @yuyiying