[discovery] Elasticsearch metrics moving to Prometheus

Hello! We are moving all our metrics from Graphite [1] to Prometheus [2]. See the master task for some details [3]. We are now working on porting all those metrics for elasticsearch [4]. This means that we'll need to update our dashboards to start using those new metrics. During the transition, I'll keep the existing dashboards, but create a copy to migrate the metrics. For example, the "Elasticsearch Percentiles" [5] dashboard has a copy named "Elasticsearch Percentiles - Prometheus" [6]. Those new dashboards should behave in just the same way, but please let me know if you find any incoherence! Have fun! Guillaume [1] https://wikitech.wikimedia.org/wiki/Graphite [2] https://wikitech.wikimedia.org/wiki/Prometheus [3] https://phabricator.wikimedia.org/T177195 [4] https://phabricator.wikimedia.org/T181627 [5] https://grafana.wikimedia.org/dashboard/db/elasticsearch-percentiles?orgId=1 [6] https://grafana.wikimedia.org/dashboard/db/elasticsearch-percentiles-promet… -- Guillaume Lederrey Operations Engineer, Discovery Wikimedia Foundation UTC+2 / CEST