Stepwise LR scheduler

[01AbhiSingh]

What does this PR do?

Fixes #<17544>

Hii @awaelchli. Can you please verify the changes I made. If they are correct then i will take up and correct any failing tests also.

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📚 Documentation preview 📚: https://pytorch-lightning--20211.org.readthedocs.build/en/20211/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81%. Comparing base (5be58f6) to head (3c48c9e).

❗ There is a different number of reports uploaded between BASE (5be58f6) and HEAD (3c48c9e). Click for more details.

HEAD has 553 uploads less than BASE

Flag	BASE (5be58f6)	HEAD (3c48c9e)
cpu	147	21
lightning	106	16
pytest	87	2
python3.9	43	6
python3.10	42	6
lightning_fabric	25	0
gpu	4	2
python3.11	42	6
python3.12	20	3
pytorch2.1	38	12
pytest-full	64	21
pytorch2.3	9	3
pytorch_lightning	20	7
pytorch2.2	9	3
pytorch2.4	8	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #20211     +/-   ##
=========================================
- Coverage      89%      81%     -8%     
=========================================
  Files         267      264      -3     
  Lines       23084    23029     -55     
=========================================
- Hits        20585    18618   -1967     
- Misses       2499     4411   +1912     

[01AbhiSingh]

Hii @Borda. Do I need to make any kind of changes in the PR ?

[lantiga]

This looks good, thank you for the contribution @01AbhiSingh

Ideally we could add a test to verify the behavior described in #17544. The current test suite can't detect the current change and this is usually a sign of insufficient coverage. Would you be willing to contribute such test?

[01AbhiSingh]

Yes, sure let me look into it.