Add support for Llama-2-70b-chat-hf in transformers
### Model description

Not sure if it is a bug, or that it is intentionally not supported yet. In either case: there have been 0 confirmations of people being able to successfully run the official **Llama-2-70b-chat-hf** model in transformers.

### Open source status

- [ ] The model implementation is available
- [X] The model weights are available

### Provide useful links for the implementation

Official model weights:
https://huggingface.co/meta-llama/Llama-2-70b-chat-hf
Related open bug:
https://github.com/facebookresearch/llama/issues/423
Turns out the model is supported, but has a bug in the `config.json`, see https://github.com/facebookresearch/llama/issues/423
Also, I am adding a version that works without any manual changes here: https://huggingface.co/daryl149/llama-2-70b-chat-hf