Prevent over allocating for group-by reduce

[Jackie-Jiang]

When a group-by query has very large LIMIT, we over-allocate the array even if there are not that many records returned.

This PR:

• Allocate array based on both the LIMIT and number of records returned
• Short-circuit the calculation when there is no record returned, or LIMIT is 0

[codecov-commenter]

Codecov Report

Merging #8921 (a7ceb17) into master (52bf09d) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #8921      +/-   ##
============================================
+ Coverage     69.73%   69.79%   +0.05%     
+ Complexity     4856     4606     -250     
============================================
  Files          1809     1809              
  Lines         94331    94337       +6     
  Branches      14069    14070       +1     
============================================
+ Hits          65784    65841      +57     
+ Misses        23970    23924      -46     
+ Partials       4577     4572       -5     

Flag	Coverage Δ
integration1	26.69% <100.00%> (-0.01%)	⬇️
integration2	25.07% <100.00%> (+0.19%)	⬆️
unittests1	66.37% <71.42%> (-0.02%)	⬇️
unittests2	14.88% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...not/core/query/reduce/GroupByDataTableReducer.java	89.86% <100.00%> (+0.42%)	⬆️
...ore/query/scheduler/resources/ResourceManager.java	84.00% <0.00%> (-12.00%)	⬇️
...ache/pinot/core/operator/docidsets/OrDocIdSet.java	86.36% <0.00%> (-11.37%)	⬇️
.../predicate/NotEqualsPredicateEvaluatorFactory.java	73.07% <0.00%> (-5.77%)	⬇️
.../pinot/core/query/scheduler/PriorityScheduler.java	78.08% <0.00%> (-5.48%)	⬇️
...ntroller/helix/core/minion/TaskMetricsEmitter.java	86.04% <0.00%> (-4.66%)	⬇️
...ion/function/DistinctCountAggregationFunction.java	44.84% <0.00%> (-4.49%)	⬇️
...controller/helix/core/minion/PinotTaskManager.java	67.29% <0.00%> (-1.58%)	⬇️
...e/pinot/segment/local/io/util/PinotDataBitSet.java	95.62% <0.00%> (-1.46%)	⬇️
.../helix/core/realtime/SegmentCompletionManager.java	72.30% <0.00%> (-0.82%)	⬇️
... and 21 more

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