Updated inference code and squad scripts
Signed-off-by: Virginia Adams <vadams@nvidia.com>

# What does this PR do ?

1. Updates squad preprocessing script and adds squad metric calculation script
2. Updates prompt learning inference script to write prediction to file
3. Turns off sequence parallel for GPT models trained with it

**Collection**: NLP

# Changelog 
- Update squad preprocessing script
- Add squad metric calculation script
- Updates GPT prompt learning model class
- Updates prompt learning GPT eval script
-  Updates T5 prompt learning model class
- Updates prompt learning T5 eval script

# Usage
* You can potentially add a usage example below

Updated gpt prompt learning eval command
```
python megatron_gpt_prompt_learning_eval.py \
            virtual_prompt_model_file=PATH_TO_NEMO_PROMPT_LEARNING_MODEL_FILE \
            gpt_model_file=PATH_TO_FROZEN_GPT_MODEL_FILE \
            inference.greedy=True \
            inference.add_BOS=False \
            trainer.devices=1 \
            trainer.num_nodes=1 \
            tensor_model_parallel_size=1 \
            pipeline_model_parallel_size=1 \
            pred_file_path=PATH_WHERE_PRED_TEXT_FILE_WILL_BE_SAVED \
            data_paths=[path/to/dataset1.jsonl, path/to/dataset2.jsonl]

```

Squad metric calculation script

```
python squad_metric_calc.py --ground-truth squad_test_gt.jsonl --preds squad_20B_preds.txt
```

# Before your PR is "Ready for review"
**Pre checks**:
- [ ] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [ ] 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)