Add CPU & Memory metrics to k8s cluster page

Description

As a first step towards https://gitlab.com/gitlab-org/gitlab-ce/issues/27890, we should show some basic health metrics about the cluster.

We should include:

• CPU Cores Used vs. Available
• Memory % Used vs. Available
• gitlab-ce~992792 would be to also provide a series for requested CPU/Memory as well.
• Pod limit (currently 100 per Node)

100% utilization in this case would be all Cores/RAM available within the cluster. (Summarization of the Node CPU/RAM)

If we can achieve this, we will be delivering more value than what can be obtained easily via the k8s console.

Proposal

We can gather the % used today, but to gather the amount requested we will need to deploy kube-state-metrics.

The general actions:

• Deploy kube-state-metrics along with Prometheus for managed clusters. If a cluster already had Prometheus deployed, we should deploy this as well. We will need to think about the scaling needs.
• Add the charts to the cluster management page. Will need UX input on this.