Add new args to BatchSizeFinder

[SkafteNicki]

What does this PR do?

Fixes #21154
Fixes #20447
Fixes #20231
Fixes #20614

Adds two new arguments to batch size finder: margin which for mode="binsearch" will reduce the found batch size to int(found_batch_size * (1-margin)) to make sure there is some room for GPU allocation afterwards. The first 3 issues linked are different scenarios related to the fact that binsearch sometimes can find a batch size that just barely fits and then when training starts it crashes immediately because the found batch size does not fit in memory anymore.

The second argument added max_val is a simple way for users to specify a maximum batch size that can be found. One case for this arg is to make sure the algorithm does not search for a batch size larger than the dataset.

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📚 Documentation preview 📚: https://pytorch-lightning--21163.org.readthedocs.build/en/21163/

[Borda]

@SkafteNicki, there are about 9 failing tests...

[SkafteNicki]

putting on hold until #21187 is merged