feat: allow immutable file upload for wandb logger

[cgebbe]

What does this PR do?

Current Problem

• given wandblogger with log_models=True and e.g. one ModelCheckpoint with save_top_k=3
• when finalizing a run
• then many models will be uploaded to wandb and beforehand copied to a local temporary directory
• and this copying can easily lead to a full disk space and thus a failed run.

Solution

• Allow to specify immutable as policy for add_file to prevent copying.

Open questions

• I didn't add a test, since the wandb logger is a stub and this feels like a very safe modification. Is that okay? Otherwise, what do you suggest?

Before submitting

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• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

PR review

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📚 Documentation preview 📚: https://pytorch-lightning--20193.org.readthedocs.build/en/20193/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79%. Comparing base (ea59e40) to head (6c022d0).

❗ There is a different number of reports uploaded between BASE (ea59e40) and HEAD (6c022d0). Click for more details.

HEAD has 146 uploads less than BASE

Flag	BASE (ea59e40)	HEAD (6c022d0)
cpu	59	24
lightning_fabric	10	0
pytest	37	0
python3.9	17	6
lightning	45	18
python3.10	8	3
python3.11	16	6
python3.12.7	18	9
gpu	2	0

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #20193     +/-   ##
=========================================
- Coverage      88%      79%     -9%     
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  Files         267      264      -3     
  Lines       23380    23326     -54     
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- Hits        20481    18367   -2114     
- Misses       2899     4959   +2060