expose task finish time via debug API

[klsince]

Refine the tasks/debug API a bit to also expose the task FinishTime.

[codecov-commenter]

Codecov Report

Merging #9534 (05e7c72) into master (e1aa147) will decrease coverage by 1.24%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #9534      +/-   ##
============================================
- Coverage     69.87%   68.63%   -1.25%     
+ Complexity     5202     4865     -337     
============================================
  Files          1927     1927              
  Lines        102693   102703      +10     
  Branches      15586    15587       +1     
============================================
- Hits          71760    70489    -1271     
- Misses        25873    27164    +1291     
+ Partials       5060     5050      -10     

Flag	Coverage Δ
integration1	26.00% <0.00%> (+0.02%)	⬆️
integration2	?
unittests1	67.23% <ø> (-0.01%)	⬇️
unittests2	15.57% <0.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
...lix/core/minion/PinotHelixTaskResourceManager.java	41.43% <0.00%> (-0.04%)	⬇️
...t/core/plan/StreamingInstanceResponsePlanNode.java	0.00% <0.00%> (-100.00%)	⬇️
...ore/operator/streaming/StreamingResponseUtils.java	0.00% <0.00%> (-100.00%)	⬇️
...server/starter/helix/SegmentReloadStatusValue.java	0.00% <0.00%> (-100.00%)	⬇️
.../operator/blocks/results/MetadataResultsBlock.java	0.00% <0.00%> (-100.00%)	⬇️
...ager/realtime/PeerSchemeSplitSegmentCommitter.java	0.00% <0.00%> (-100.00%)	⬇️
...urces/ServerReloadControllerJobStatusResponse.java	0.00% <0.00%> (-100.00%)	⬇️
...he/pinot/common/utils/grpc/GrpcRequestBuilder.java	0.00% <0.00%> (-90.91%)	⬇️
...ator/streaming/StreamingSelectionOnlyOperator.java	0.00% <0.00%> (-90.00%)	⬇️
...he/pinot/core/plan/StreamingSelectionPlanNode.java	0.00% <0.00%> (-88.89%)	⬇️
... and 145 more

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