Fix default value for enable_progress_bar in docs

[JiahaoYao]

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[Borda]

in fact, I think we shall remove all defaults from docstring as it duplicates of function footprint and source os misalignments...

[akihironitta]

@Borda There was a similar comment #11614 (comment) by @awaelchli.

Currently, the sphinx doc generator adds the default values automatically to the rendered docs page based on the default values specified in the signature. We have discussed manually adding these for each parameter in the past, like you did here. The maintenance effort is higher: when a default value changes, it needs to be updated manually in the docstring too. But considering that the trainer defaults don't change very often, and it is sometimes hard to read the docs, I am fine with either way :)

For the rest of the code base, I would let sphinx handle the defaults.

I'm fine with either way, too.