Allow separate config files for parameters with class type when LightningCLI is in subclass_mode=False

[mauvilsa]

What does this PR do?

This enables the possibility of having separate config files for parameters whose type hint is a class when the LightningCLI is in subclass_mode=False. For subclass_mode=True this option is enabled by default so this change also makes it more consistent.

For example for a CLI like:

from torchaudio.transforms import MelSpectrogram
from pytorch_lightning.utilities.cli import LightningCLI
import pytorch_lightning as pl

class PrxMelDataModule(pl.LightningDataModule):
    def __init__(self, mel_spec: MelSpectrogram):
        ...

class HifiGAN(pl.LightningModule):
    def __init__(self, mel_spec: MelSpectrogram):
        ...

if __name__ == "__main__":
    LightningCLI(
        model_class=HifiGAN,
        datamodule_class=PrxMelDataModule,
    )

it would be possible to have a config like:

data:
  mel_spec: mel_spec_config.yml
model:
  mel_spec: mel_spec_config.yml

Fixes omni-us/jsonargparse#95 (comment)

Does your PR introduce any breaking changes? If yes, please list them.

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[tchaton]

Dear @mauvilsa,

We are releasing v1.5 by tomorrow. Do you believe you could get this PR by then ?

Best,
T.C

[mauvilsa]

We are releasing v1.5 by tomorrow. Do you believe you could get this PR by then ?

Yes, sure. This is a small change.

[tchaton]

LGTM !

[ethanwharris]

LGTM 😃