GPT multinode eval
# What does this PR do ?

This PR adds multi-node eval for GPT. Also, it adds the ability to do GPT eval from PTL checkpoint. This is useful when models are very large.

**Collection**: NLP

# Usage
```python
python /code/examples/nlp/language_modeling/megatron_gpt_eval.py \
	--devices ${SLURM_NTASKS_PER_NODE} \
	--num_nodes ${SLURM_JOB_NUM_NODES} \
	--checkpoint_dir "/checkpoint_dir" \
	--checkpoint_name ${CHECKPOINT_NAME} \
	--hparams_file /hparams_dir/${HPARAMS_FILE} \
	--prompt "In critical moments, people sometimes see exactly"  \
	--tensor_model_parallel_size ${TENSOR_MODEL_PARALLEL_SIZE} \
	--pipeline_model_parallel_size ${PIPELINE_MODEL_PARALLEL_SIZE} \
	--tokens_to_generate 32 \
	--stop_after_sentence True \
	--precision ${PRECISION}
```

# Before your PR is "Ready for review"
**Pre checks**:
- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [x] Did you write any new necessary tests?
- [x] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [x] New Feature
- [ ] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


## Who can review?

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)
