Flexible and easy to use HSDP setting

[Liyang90]

What does this PR do?

Fixes #19502

It allows users to provide device_mesh as a tuple to the FSDPStrategy.

The test case for hybrid fsdp strategy would be broken, because _init_sharding_strategy is moved out of the __init__ function.

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📚 Documentation preview 📚: https://pytorch-lightning--19504.org.readthedocs.build/en/19504/

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 6 lines in your changes missing coverage. Please review.

Project coverage is 59%. Comparing base (1a6786d) to head (949d36f).
Report is 97 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (1a6786d) and HEAD (949d36f). Click for more details.

HEAD has 188 uploads less than BASE

Flag	BASE (1a6786d)	HEAD (949d36f)
python3.10	23	15
cpu	91	43
lightning	55	31
pytest	71	26
examples	9	0
app	9	0
lightning_fabric	19	8
python3.11	34	16
python3.8	18	12
pytorch2.0	12	11
pytest-full	24	21
pytorch_lightning	10	8
pytorch2.1	6	5
pytorch2.3	3	2
lightning_app	2	0

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #19504     +/-   ##
=========================================
- Coverage      84%      59%    -25%     
=========================================
  Files         426      421      -5     
  Lines       35264    35182     -82     
=========================================
- Hits        29553    20772   -8781     
- Misses       5711    14410   +8699     

[awaelchli]

Great job. Looking forward to this feature.

[npuichigo]

Any updates on this?

[Liyang90]

Hi @awaelchli , I just fixed a merge conflict with the master and pushed the change. Could you take another look? Let me know if you have any concerns.

[Liyang90]

All checks have passed. But I don't have access to merge the PR.

[awaelchli]

@Liyang90 Thank you for contributing this, and apologies for the delay.
I allowed myself to push a minor change regarding the import and extending the test.