Support TQDM_MINITERS env variable

[wouterzwerink]

What does this PR do?

Fixes #19346

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📚 Documentation preview 📚: https://pytorch-lightning--19381.org.readthedocs.build/en/19381/

[codecov]

Codecov Report

Merging #19381 (4cd09f7) into master (6421dd8) will decrease coverage by 35%.
Report is 1 commits behind head on master.
The diff coverage is 100%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #19381      +/-   ##
==========================================
- Coverage      84%      49%     -35%     
==========================================
  Files         448      440       -8     
  Lines       37885    37734     -151     
==========================================
- Hits        31647    18364   -13283     
- Misses       6238    19370   +13132     

[awaelchli]

Thanks @wouterzwerink for making the pull request.
I pushed a unit test for good measure :)