Monitoring mixins

[pavolloffay]

From https://github.com/jaegertracing/jaeger-analytics-java/pull/22/files/9e685d50c76bdf9c61a4917044ecf39a5b5de3cd#diff-f80ad592b359d09d6eef8e113412a26b use monitoring mixins for Grafana dashboards and prometheus alerts. At the moment we host only dashboards, once the complexity rises we should consider using mixins.

A monitoring mixin is a package of configuration containing Prometheus alerts, Prometheus recording rules and Grafana dashboards.

https://docs.google.com/document/d/1A9xvzwqnFVSOZ5fD3blKODXfsat5fg6ZhnKu9LK3lB4/view#
https://docs.google.com/document/d/1oXfthGcAOMriy7PEqrq_E8ecz1U_Jyn3QYqEWoHN7S8/edit#heading=h.rfr677ib684e