Fix to allow custom CheckpointIO with strategy classes

[rohitgr7]

What does this PR do?

Earlier since we initialized accelerator specific CheckpointIO in the strategy init, user's don't have an option to plugin custom CheckpointIO due to this:
https://github.com/Lightning-AI/lightning/blob/0e5312833fa70fb744f316f3db19c78b38eb9683/src/pytorch_lightning/trainer/connectors/accelerator_connector.py#L348-L352

Found while working on #13658

Does your PR introduce any breaking changes? If yes, please list them.

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cc @Borda @awaelchli @ananthsub @ninginthecloud @rohitgr7 @otaj @akihironitta

[rohitgr7]

need help with mypy

[codecov]

Codecov Report

Merging #13785 (12f0ac0) into master (4588a79) will increase coverage by 27%.
The diff coverage is 74%.

@@            Coverage Diff            @@
##           master   #13785     +/-   ##
=========================================
+ Coverage      49%      76%    +27%     
=========================================
  Files         327      327             
  Lines       25457    25540     +83     
=========================================
+ Hits        12437    19499   +7062     
+ Misses      13020     6041   -6979     

[kaushikb11]

Thanks!