Update pytorch_lightning to pytorch.lightning when bumping NeMo version

[jstjohn]

This will be required for our next version bump. All instances of pytorch_lightning in imports need to change to pytorch.lightning. We may also need to look at dependencies.

More info from a slack thread I am pasting below:

NVIDIA/NeMo#11306 and NVIDIA/NeMo#11252 have been merged, which replace all usage of pytorch_lightning with lightning.pytorch . pytorch_lightning should no longer be present in the container.
Going forward if you need to import something from Lightning, use import lightning.pytorch , import lightning.fabric , or from lightning... import ....
If you use import pytorch_lightning you'll likely see a ModuleNotFoundError, or errors similar to the one reported in this thread, especially if you try to inherit from pytorch_lightning .
Please see PRs for context.