API to expose the count of active task executions on minion

[shounakmk219]

Description

Expose an API that provides the value of MinionGauge.NUMBER_OF_TASKS gauge which corresponds to the number of active task executions going on the minion.

Path : /tasks/active/count Method : GET Sample response:

{
  "activeTasksCount": 10
}

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 61.96%. Comparing base (59551e4) to head (2586796). Report is 782 commits behind head on master.

Files	Patch %	Lines
...nion/api/resources/PinotMinionMetricsResource.java	0.00%	9 Missing :warning:
...g/apache/pinot/common/metrics/AbstractMetrics.java	0.00%	2 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #13550      +/-   ##
============================================
+ Coverage     61.75%   61.96%   +0.21%     
+ Complexity      207      198       -9     
============================================
  Files          2436     2554     +118     
  Lines        133233   140482    +7249     
  Branches      20636    21852    +1216     
============================================
+ Hits          82274    87054    +4780     
- Misses        44911    46797    +1886     
- Partials       6048     6631     +583     

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[shounakmk219]

That makes sense. Will make the changes accordingly.

[shounakmk219]

@Jackie-Jiang I explored the option of having an endpoint to get metric values. There were lot of other complications around it hence decided to stick to the existing API just instead of relying on the gauge metric it fetches the active tasks count using MinionEventObservers

[shounakmk219]

@Jackie-Jiang based on your inputs updated the code to expose just the gauge values for now.