Add account level metrics for container metrics

[justinlin-linkedin]

Summary

Add account level metric to aggregate its containers' metrics.

Details

Some accounts have lots of containers and it's very hard those those accounts to aggregate all the metrics for 40x, 50x and latency etc. This PR adds an AccountMetrics class and have its ContainerMetrics to record metrics for AccountMetrics.

This PR also adds a configuration to only enable some accounts to have this AccountMetrics as most accounts have very small set of containers that they just don't need extra metrics.

Test

Unit test

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.17544% with 17 lines in your changes missing coverage. Please review.

Project coverage is 70.26%. Comparing base (52ba813) to head (a6fb9fc). Report is 128 commits behind head on master.

Files with missing lines	Patch %	Lines
.../github/ambry/frontend/EntityOperationMetrics.java	69.23%	9 Missing and 3 partials :warning:
...java/com/github/ambry/frontend/AccountMetrics.java	0.00%	2 Missing :warning:
...va/com/github/ambry/frontend/ContainerMetrics.java	60.00%	1 Missing and 1 partial :warning:
...github/ambry/frontend/RestRequestMetricsGroup.java	83.33%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2926      +/-   ##
============================================
+ Coverage     64.24%   70.26%   +6.01%     
- Complexity    10398    11982    +1584     
============================================
  Files           840      866      +26     
  Lines         71755    73711    +1956     
  Branches       8611     8870     +259     
============================================
+ Hits          46099    51793    +5694     
+ Misses        23004    19212    -3792     
- Partials       2652     2706      +54     

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