Separate Training and Validation Batch Sizes
Signed-off-by: Virginia Adams <vadams@nvidia.com>

Makes training and validation batch sizes separately configurable for T5 prompt learning. Related to https://jirasw.nvidia.com/projects/NLP/issues/NLP-393?filter=allopenissues

**Collection**: NLP

# Changelog 
- Add specific line by line info of high level changes in this PR.

# Usage

```python
 data:
    add_eos: true
    add_bos: false
    decoder_starts_with_pad: False
    add_eos_to_decoder_output: True
    add_sentinel_to_input: True
    ul2_prompt_token: null # <extra_id_s>, <extra_id_r>, <extra_id_x>

    train_ds: 
      path: ["data/squad_train.jsonl"]
      global_batch_size: 8
      micro_batch_size: 8 # micro batch size should equal global batch size when pipeline parallel = 1
      shuffle: true
      num_workers: 4
      pin_memory: true

    validation_ds: 
      path: ["data/squad_val.jsonl"]
      global_batch_size: 8
      micro_batch_size: 8 # micro batch size should equal global batch size when pipeline parallel = 1
      shuffle: true
      num_workers: 4
      pin_memory: true
```

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

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# Additional Information
* Related to # (issue)
