Unbabel-comet

Minor fixes that address issues 177, 178, 185, 183 and 191

Release of [xCOMET models](https://arxiv.org/pdf/2310.10482.pdf)!

To make it easier to merge with internal code we added a new class [XCOMETMetric](https://github.com/Unbabel/COMET/blob/v2.2.0/comet/models/multitask/xcomet_metric.py#L33C7-L33C19). This release only allows inference of such models. Training is still not fully implemented.

Models can be accessed through hugging face hub:
- [XCOMET-XL](https://huggingface.co/Unbabel/XCOMET-XL)
- [XCOMET-XXL](https://huggingface.co/Unbabel/XCOMET-XXL)

Minor bug fix on MBR default model.
Rollback to CometKiwi-22 as default QE model (due to being lightweight)
Minor dependencies update

Released of CometKiwi [-XL](https://huggingface.co/Unbabel/wmt23-cometkiwi-da-xl) and [-XXL](https://huggingface.co/Unbabel/wmt23-cometkiwi-da-xxl)

Bump torchmetrics ("^0.10.2") and Pytorch Lightning ("^2.0.0") (159)

Update on MODELS.md and LICENSE.models.md documentation.

Minor bug fix, update HF hub and released [CometKiwi model](https://huggingface.co/Unbabel/wmt22-cometkiwi-da):
- Bump Hugging Face Hub (^0.16.0)
- Added flexibility to checkpoint download (156 )
- [CometKiwi](https://huggingface.co/Unbabel/wmt22-cometkiwi-da) model is finally released. It's open-source with a non-commercial license.