[CELEBORN-1626] group mapTask

[zaynt4606]

What changes were proposed in this pull request?

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[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 32.17%. Comparing base (165e914) to head (41fba8d).
Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
...born/common/protocol/message/ControlMessages.scala	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2771      +/-   ##
==========================================
- Coverage   32.35%   32.17%   -0.17%     
==========================================
  Files         329      329              
  Lines       19511    19697     +186     
  Branches     1752     1774      +22     
==========================================
+ Hits         6311     6336      +25     
- Misses      12855    13015     +160     
- Partials      345      346       +1     

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[github-actions]

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[mridulm]

I dont think this CIP was discussed in the mailing list - was it ? I want to make sure I did not miss the details !
Essentially I am trying to understand how much config tuning would help, what is the space of problems where map side grouping would benefit, and how we can transition from one to the other reasonably.