Do not force sync_dist=True on epoch end

[krishnakalyan3]

Fixes #13210

Just FYI, with fault-tolerant training, we need to ensure sync happens because during a failure on, let's say, a spot instance, the metrics are synced and saved to the checkpoint, so during restart, metrics on rank 0 are from the accumulated ones from the previous run, and on other ranks, they are 0. So we need to make sure they are synced in further training to ensure correct calculation.

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[krishnakalyan3]

Thank you @rohitgr7. It was really nice learning from you.
Thanks for the reviews @carmocca and @otaj

[codecov]

Codecov Report

Merging #13364 (105ee0a) into master (9596fab) will decrease coverage by 10%.
The diff coverage is 86%.

@@            Coverage Diff            @@
##           master   #13364     +/-   ##
=========================================
- Coverage      86%      76%    -10%     
=========================================
  Files         327      327             
  Lines       25500    25505      +5     
=========================================
- Hits        21898    19455   -2443     
- Misses       3602     6050   +2448