* Add tier based usage metrics for historical nodes to help with druid historical autoscaling
Add tier based usage metrics for historical nodes to help druid cluster orchestration systems understand the historical node usage and requirements. Following metrics would be helpful -
tier/required/capacity- total capacity in bytes required in each tier. Dimensions - tier
tier/total/capacity - total capacity in bytes available in a given tier. Dimension - tier
tier/historical/count - no. of historical nodes available in each tier. Dimension - tier
tier/replication/factor - configured maximum replication factor in given tier. Dimension - tier
* fix unit test failures
* fix segment underReplicated/unavailable counts to be gauges instead of counters
* fix jvm/gc/cpu to be a counter instead of timre
jvm/gc/cpu represents the total cpu time spent for multiple gc
invocations, not the time spent in each gc cycle.
the number needs to be divided by jvm/gc/count to get the average gc
time per cycle
* update docs
* fix spellcheck
Gian Merlino
Nishant Bangarwa
Xavier Léauté
Chi Cao Minh