Update LR step scheduler to use total step to work across epochs

[falckt]

What does this PR do?

Fixes #17544

I am not sure whether to consider this as a breaking change. For frequencies > epoch length I would consider it a bug fix. For frequencies < epoch length it does change the behavior but IMHO not in a fundamental way and personally I expected the new behavior to begin with.

Before submitting

• Was this discussed/agreed via a GitHub issue? change according to @awaelchli suggestion in Stepwise LR-Scheduler not working across epochs  #17544 (comment)

• Did you read the contributor guideline, Pull Request section?

• Did you make sure your PR does only one thing, instead of bundling different changes together?

• Did you make sure to update the documentation with your changes?

  I don't think it is necessary, I would consider the new behavior the expected one.

• Did you write any new necessary tests?

  I couldn't find any tests for the old code. Q: does this need a test?

• Did you verify new and existing tests pass locally with your changes? it works as expected locally

• Did you list all the breaking changes introduced by this pull request? yes

• Did you update the CHANGELOG? todo

PR review

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📚 Documentation preview 📚: https://pytorch-lightning--20248.org.readthedocs.build/en/20248/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81%. Comparing base (474bdd0) to head (fd1883f).
Report is 1 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (474bdd0) and HEAD (fd1883f). Click for more details.

HEAD has 87 uploads less than BASE

Flag	BASE (474bdd0)	HEAD (fd1883f)
cpu	41	21
python3.10	12	6
lightning_fabric	7	0
pytest	25	2
lightning	31	16
python3.9	11	6
gpu	4	2
python3.11	12	6
python3.12	6	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #20248     +/-   ##
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- Coverage      89%      81%     -8%     
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  Files         267      264      -3     
  Lines       23064    23009     -55     
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- Hits        20573    18606   -1967     
- Misses       2491     4403   +1912     

[lantiga]

Thank you @falckt !
This is a duplicate of #20211 (for fairness the other PR came first : )
maybe you can help with a test there?