migrate from appdirs to platformdirs

[skshetry]

appdirs has been deprecated/unmaintained, platformdirs is now recommended. Closes #9130.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (9101fce) 92.90% compared to head (88ed200) 92.90%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9131      +/-   ##
==========================================
- Coverage   92.90%   92.90%   -0.01%     
==========================================
  Files         456      456              
  Lines       36810    36810              
  Branches     5311     5211     -100     
==========================================
- Hits        34199    34197       -2     
- Misses       2086     2089       +3     
+ Partials      525      524       -1     

Impacted Files	Coverage Δ
dvc/config.py	98.51% <100.00%> (ø)
tests/conftest.py	78.03% <0.00%> (-5.31%)	⬇️
dvc/repo/experiments/queue/celery.py	87.50% <0.00%> (+1.83%)	⬆️

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