AWS Neuron support

Nobody has claimed this yet.

## 🚀 Feature

https://awsdocs-neuron.readthedocs-hosted.com/en/latest/index.html
https://aws.amazon.com/machine-learning/neuron/

### Motivation

https://aws.amazon.com/about-aws/whats-new/2022/10/ec2-trn1-instances-high-performance-cost-effective-deep-learning-training/

### Pitch

Neuron is XLA based, so it'll probably be an accelerator and strategy. Their marketing materials also advertise that it supports FSDP, and Megatron-LM. It's unclear at this point whether we would have specialized Neuron-based implementations for those.

We would also need access to hardware for testing.

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- [**Metrics**](https://github.com/Lightning-AI/metrics): Machine learning metrics for distributed, scalable PyTorch applications.

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- [**Flash**](https://github.com/Lightning-AI/lightning-flash): The fastest way to get a Lightning baseline! A collection of tasks for fast prototyping, baselining, fine-tuning, and solving problems with deep learning.

- [**Bolts**](https://github.com/Lightning-AI/lightning-bolts): Pretrained SOTA Deep Learning models, callbacks, and more for research and production with PyTorch Lightning and PyTorch.

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Start by reading the linked AWS Neuron documentation and the Neuron hardware requirements. Determine the integration points for an XLA-based accelerator or strategy, including whether FSDP or Megatron-LM need specialized implementations; completion would require an agreed design, implementation, and access to Neuron hardware for testing.

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