Rename metric names & help to follow best pratices
Rename metric names & help to follow best pratices

ewr/elasticsearch_exporter,jrummler/elasticsearch_exporter,William-Yeh/es_cluster_exporter,yackushevas/elasticsearch_exporter,mattkanwisher/elasticsearch_exporter,Kuckkuck/elasticsearch_exporter,rayhou/elasticsearch_exporter,justwatchcom/elasticsearch_exporter