Bump version of pytorch-lightning to 2.0.0

[eschibli]

Fixes #2086

Summary

Changed torch requirements to require pytorch-lightning>=2.0 due to dependency on ProgressBar

[dennisbader]

Hi @eschibli and thanks for this fix.

It might be a bit early for us to discard lightning<2.0.0.

What I would suggest is to adapt the ProgressBar import in darts.models.forecasting.torch_forecasting_model.py.

Move the progressbar import in this line into the version specific imports from here:

if pl_200_or_above:
    from pytorch_lightning.tuner import Tuner
    from pytorch_lightning.callbacks import ProgressBar
else:
    from pytorch_lightning.tuner.tuning import Tuner
    from pytorch_lightning.callbacks import ProgressBarBase

[dennisbader]

Hi @eschibli. I applied the changes already, as we want to release a patch for this soon.
Thanks again for your contribution 🚀

[dennisbader]

LGTM, thanks @eschibli 🚀 💯