Nicer logging of list of dicts for hyper parameters

[vork]

What does this PR do?

Currently, when hyper parameters are logged with log_hyperparams the function calls _flatten_dict to collapse the dict to a single level. However, when the config contains a list of dicts, this gets flattened to a single string. Instead I would propose to log the list as [key/0/item, key/1/item] etc.

Fixes #19957

Before submitting

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  Only a minor change
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  This does not require any changes just makes the hyper parameter logging slightly nicer
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📚 Documentation preview 📚: https://pytorch-lightning--19963.org.readthedocs.build/en/19963/

[jammm]

@lantiga @Borda @tchaton @justusschock it would be great if you can take a look at this PR ^^

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88%. Comparing base (96df8c4) to head (9fc3e1c).
Report is 114 commits behind head on master.

Additional details and impacted files

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  Coverage      88%      88%           
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  Files         267      267           
  Lines       23355    23358    +3     
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+ Hits        20458    20461    +3     
  Misses       2897     2897