Add ModelOpt QAT example for Llama2 SFT model
Can we enable the gradient/activation checkpointing from Nemo trainer? This will make the GPU memory requirement for QAT similar to that of original finetuning. @realAsma should we disable FP8 KV cache for INT4 weight only?

| FP8 KV Cache | PTQ | QAT |
| --------|-------|-------- |
| Enabled | 1.345 | 1.216 |
| Disabled | 1.305 | 1.172 |

BF16 baseline is 1.15 LGTM; > @realAsma should we disable FP8 KV cache for INT4 weight only?
> 
> FP8 KV Cache	PTQ	QAT
> Enabled	1.345	1.216
> Disabled	1.305	1.172
> BF16 baseline is 1.15

That depends on how easy it is to enable KV cache quantization from the config file. If it is easy to do, sure we can enable. However this might not have huge value if there are already good PTQ examples demonstrating KV cache quantization. > That depends on how easy it is to enable KV cache quantization from the config file. If it is easy to do, sure we can enable. However this might not have huge value if there are already good PTQ examples demonstrating KV cache quantization.

We currently don't have KV cache quantization parameter in config and its enabled by default for all except int8_sq.

For INT4 having it enabled (default) makes QAT look less appealing as we are still a bit off from bf16 so I though it would be better to disable it.

Let me make if a config parameter and disable it for now -- maybe speedup may be lower LGTM!
# What does this PR do ?
- Add an example for doing Quantization aware Training (QAT) for Llama SFT model.
- Requires https://github.com/NVIDIA/NeMo/pull/9276 to be merged first

**Collection**: nlp
- `nemo/collections/nlp/parts/nlp_overrides.py` is modified to save/restore model optimizer sharded state to the .nemo checkpoint

# Changelog 
- Add support to save model optimizer's quantization state to the `.nemo` checkpoint (similar support is already merged to Megatron-LM) to save/resume PyTorch Quantization state before TRT-LLM export is done
- Add an example to perform Quantization-aware training (QAT) for the Llama2 SFT Model
- Updated necessary documentation
- Add INT4 QAT CI test 
- Upgrade ModelOpt version from 0.11 to 0.13

# Usage
```bash
python examples/nlp/language_modeling/tuning/megatron_gpt_qat.py \
  quantization.algorithm=fp8 \
  quantization.num_calib_size=8 \
  trainer.devices=1 \
  trainer.num_nodes=1 \
  trainer.max_steps=4 \
  trainer.val_check_interval=4 \
  +trainer.limit_val_batches=2 \
  exp_manager.explicit_log_dir=llama2_qat_results \
  model.restore_from_path=/home/TestData/nlp/megatron_llama/llama_ci.nemo \
  model.tensor_model_parallel_size=1 \
  model.pipeline_model_parallel_size=1 \
  model.global_batch_size=2 \
  model.data.train_ds.file_names=[/home/TestData/nlp/megatron_sft/quarel.jsonl] \
  model.data.train_ds.concat_sampling_probabilities=[1.0]
  model.data.validation_ds.file_names=[/home/TestData/nlp/megatron_sft/quarel.jsonl] \
```

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