Customizations for node-exporter collectors

Proposed title of this feature request

node-exporter collector customizations

What is the nature and description of the request?

We've had several requests and efforts in the past to change, add or drop certain collectors in our node-exporter statefulset. This feature requests intends to subsume the individual requests and channel these efforts into a cohesive feature that will serve the original requests and ideally address future needs.

We are going to add a section for Node Exporter into the CMO config. Each customizable collector has its dedicated subsection containing its own parameters under the NodeExporter section. The config map looks like the example below.

apiVersion: v1
kind: ConfigMap
metadata: 
  name: cluster-monitoring-config
  namespace: openshift-monitoring
data: 

  config.yaml: |

    nodeExporter: 
      collectors: 
        # disable a collector which is enabled by default
        netclass: 
          enabled: false
        # enable a collector which isn't enabled by default but supported by CMO.
        hwmon: 
          enabled: true
        # tweak the configuration of a collector
        netdev: 
          enabled: true
          ignoredDevices: 
            - br-.+
            - veth.*
          fooBar: xxx # unrecognized parameter will be ignored.
        # trying to disable unsupported collectors or turning off mandatory collectors will be ineffective too
        # as the keys wouldn't exist in the node exporter config struct.
        drbd: {enabled: true} # unsupported collectors will be ignored and logged as a warning
        cpu: {enabled: false} # necessary collectors will not turn off and this invalid config is logged as a warning.

No web UI changes are required, all settings are saved in CMO configmap.

Users should be informed of consequences of deactivating certain collectors, such as missing metrics for alerts and dashboards.

Why does the customer need this? (List the business requirements)

See linked issues for customer requests. Ultimately this will serve to add flexibility to our stack and serve customer needs better.

List any affected packages or components.

node-exporter, CMO config