[DOC OCP] Document metrics configuration in ConfigMap instead of metrics property

  metrics:
    # Inspired by kafka-connect rules
    # https://github.com/prometheus/jmx_exporter/blob/master/example_configs/kafka-connect.yml
    lowercaseOutputName: true
    lowercaseOutputLabelNames: true
    rules:
      #kafka.connect:type=app-info,client-id="{clientid}"
      #kafka.consumer:type=app-info,client-id="{clientid}"
      #kafka.producer:type=app-info,client-id="{clientid}"
      - pattern: 'kafka.(.+)<type=app-info, client-id=(.+)><>start-time-ms'
        name: kafka_$1_start_time_seconds
        labels:
          clientId: "$2"
        help: "Kafka $1 JMX metric start time seconds"
        type: GAUGE
        valueFactor: 0.001
...

  metricsConfig:
    type: jmxPrometheusExporter
    valueFrom:
      configMapKeyRef:
        name: mirror-maker-2-metrics
        key: metrics-config.yml