[Eagle-2][Eagle-24] Eagle Metric Framework and two user cases

[Libin Sun <ab...@gmail.com>]

As a monitoring system, eagle should generate metrics of  alert, policy,
events count, kafka topic consuming speed, data distribution etc to get a
overview of the object it monitor on and it's own running states

Previously we have a simple metric framework, to make it become more
generic for our monitoring purpose, I intend to do some refactor on it,

The below is some document on metric framework design as well as for
[Eagle-2] & [Eagle-24]

https://github.com/eBay/Eagle/wiki/Eagle-Metric-Framework-Draft-Design


References:

https://github.com/dropwizard/metrics

https://www.endgame.com/blog/storm-metrics-how


Thanks
Libin