Expose OAuth2 settings for remote write in the CMO configuration

apiVersion: v1
kind: ConfigMap
metadata:
  name: cluster-monitoring-config
  namespace: openshift-monitoring
data:
  config.yaml: |
    prometheusK8s:
      remoteWrite:
      - url: "https://remote-write.endpoint"
        oauth2:
          clientId:
            secret:
              name: oauth2-credentials
              key: id
          clientSecret:
            name: oauth2-credentials
            key: secret
          tokenUrl: "https://example.com/oauth"
          scopes: []
          endpointParams: {}