Fix nemo_llama_to_hf conversion
This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days. This PR was closed because it has been inactive for 7 days since being marked as stale. This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days. jenkins
# What does this PR do ?

Fix convert_nemo_llama_to_hf.py:

- Correctly account for `megatron_amp_O2` flag
- Save HF model with correct precision
- Transfer over the NeMo tokenizer, instead of using the possibly-incompatible default tokenizer
- Make sure to save fast version of tokenizer
- Resize the model's embedding tensor to match the new tokenizer's vocab
- Correct a typo in how-to-use example

  
**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation


## Who can review?

@ericharper 

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

# Additional Information
* Related to # (issue)
