Add nemo2 conversion scripts for export
Let's add some docs and ci test then we can merge. If possible we'd like to keep the number of scripts to a minimum and instead add things like this to our CLI. You can look at [api.py](https://github.com/NVIDIA/NeMo/blob/main/nemo/collections/llm/api.py) as examples for things like train, finetune, etc. There are some usage docs [here](https://github.com/NVIDIA/NeMo/tree/main/examples/llm/pretrain). We have some docs around creating CLI-entrypoints [here](https://github.com/NVIDIA/NeMo-Run/tree/main/examples/entrypoint). This is a temporary solution for exporting nemo2 ckpt. Eventually we will integrate this into megatron, so we won't add this into api. This script has been tested by llama3-8b nemo2 checkpoint.
# What does this PR do ?

Add nemo2 conversion scripts for export

**Collection**: [Note which collection this PR will affect]

# Changelog 
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# Usage
* You can potentially add a usage example below

```python
# Add a code snippet demonstrating how to use this 
```

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