default to TAR if push mode is not set

[klsince]

Set push mode to TAR, in case the pushMode is not set explicitly in task, to be backward compatible.

[codecov-commenter]

Codecov Report

Merging #9935 (e6690dc) into master (bb83f5c) will increase coverage by 6.69%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #9935      +/-   ##
============================================
+ Coverage     27.95%   34.65%   +6.69%     
- Complexity       53      191     +138     
============================================
  Files          1970     1982      +12     
  Lines        106115   106481     +366     
  Branches      16097    16138      +41     
============================================
+ Hits          29666    36899    +7233     
+ Misses        73517    66449    -7068     
- Partials       2932     3133     +201     

Flag	Coverage Δ
integration1	25.01% <100.00%> (+0.03%)	⬆️
integration2	?
unittests2	15.83% <0.00%> (?)

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

Impacted Files	Coverage Δ
.../tasks/BaseMultipleSegmentsConversionExecutor.java	82.53% <100.00%> (+1.25%)	⬆️
.../apache/pinot/server/access/RequesterIdentity.java	0.00% <0.00%> (-100.00%)	⬇️
...g/apache/pinot/server/api/resources/ErrorInfo.java	0.00% <0.00%> (-100.00%)	⬇️
...pinot/core/data/manager/realtime/TimerService.java	0.00% <0.00%> (-100.00%)	⬇️
...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%)	⬇️
...ager/realtime/PeerSchemeSplitSegmentCommitter.java	0.00% <0.00%> (-100.00%)	⬇️
...form/function/IsDistinctFromTransformFunction.java	0.00% <0.00%> (-100.00%)	⬇️
...m/function/IsNotDistinctFromTransformFunction.java	0.00% <0.00%> (-100.00%)	⬇️
... and 517 more

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