Fixed metrics privileges and improved possibilitycustomization

[lodatol]

We tried to deploy this to out recent OKE 1.25 but we had some issues, we overcame those issue and we want to share the solution:

1. we had to explicitly mention in the cluster role the "/metrics" endpoint for the k8s cluster otherwise we would not be able to scrape some etcd and cluster aware metrics
2. the dashboard now target the new and correct metrics for container metrics
3. we added the possibility in the values.yaml to add an array of configmaps in order to give the user the possibility to extend logging analytics images configuration (i.e. modify agent.json to change uploaded metrics)