Parallel prompt tuning
# What does this PR do ?

This PR fixes prompt tuning to work with the updated pipeline parallel code. In this PR a user can also prompt tune using tensor parallel > 1.  More work will need to be done for prompt tuning to be supported for pipeline parallel > 1. 

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

# Changelog 
- prompt tuning with tp=1 and pp=1 works again with updated pipeline parallel code
- prompt tuning with tp > 1 works
- prompt tuning works with the updated complete and compute log probs methods
- Added a prompt tuning config file with prompting specific defaults set
- prompt tuning tests are add back

# Usage
```python
python examples/nlp/language_modeling/megatron_gpt_prompt_tuning.py \
    --config-name=megatron_prompt_tuning_gpt \
    restore_from_path='/prompt-tuning/megatron_gpt.nemo' \
    trainer.val_check_interval=2 \
    trainer.max_steps=5 \
    model.new_prompt_tags=['Winogrande, BoolQ'] \
    model.new_prompt_init_text=['logic choose person name, None'] \
    model.new_prompt_init_methods=['text, random'] \
    model.data.train_ds='/prompt-tuning/wino_bool_prompt_tuning_train.json' \
    model.data.valid_ds='/prompt-tuning/wino_bool_prompt_tuning_val.json' \
    +model.data.test_ds='/prompt-tuning/wino_bool_prompt_tuning_val.json' \
    model.micro_batch_size=2 \
    model.global_batch_size=4 \
    model.optim.lr=2e-2 \
    model.optim.sched.min_lr=2e-3 \
    model.optim.sched.warmup_steps=2 \
    model.optim.sched.constant_steps=8 \
    model.encoder_seq_length=2048
```

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**PR Type**:
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- [X] Bugfix
- [ ] Documentation

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# Additional Information
* Related to # (issue)
