[WIP] Integrate OSLO for tensor parallelism support
# What does this PR do?

This PR integrates [OSLO](https://github.com/tunib-ai/oslo) in a similar fashion to DeepSpeed. OSLO enables tensor parallelism and kernel fusion, among others.

## To-do
- [ ] Tests
- [ ] Adding OSLO as dependency
- [ ] Review/discuss model save logic

## Who can review?

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15737). All of your documentation changes will be reflected on that endpoint.<|||||>To-do's for self-documentation:

- [ ] Revisit `should_save`
- [ ] Test with DDP and FairScale
- [ ] Think about how to toggle `merge_checkpoint`
- [ ] Debug DeepSpeed (model param size 1)
- [ ] Use `oslo_initialized` attribute to check if OSLO was initialized MPU<|||||>Unstale<|||||>Closing due to changes in OSLO's API as discussed internally. This PR will be superseded by a future PR once OSLO 3 is released and stable.