Better model for metrics and document existing metrics

[michal-harish]

Multi-partition metrics are difficult to aggregate wehether in InfluxDb or DataDog because they are treated as separate measurments > they recommend reporting a single measurement for what needs to be viewed as a single metric.

• Kamon has good tag support but too many dependencies - the 1.x version has improved a lot in terms of dependencies but doesn't have a JMX reporter and there is no issue tracked to add it

• To get tags support with Dropwizard need to wait for this: Future of metrics 4.0 and metric tags dropwizard/metrics#1175