Release 0.2.7-adobe-20200504

ISSUE-155 Enable prometheus monitoring for zookeeper pods

Since 3.6.0 ZooKeeper supports native Prometheus monitoring
https://github.com/apache/zookeeper/blob/master/zookeeper-docs/src/main/resources/markdown/zookeeperMonitor.md#prometheus

This patch
- enables `PrometheusMetricsProvider` in zoo.cfg
- expose a new `metrics` port to ZK pods, ZK services
- disambiguate the headless and client service labels by adding a new label,
 so it can be used in Prometheus `ServiceMonitors`