Packed sequence data shuffling & without `thd` attention
jenkins jenkins
# What does this PR do ?

Enable 1) data shuffling for packed sequence dataset, and
2) packed sequence with normal attention kernel (no `thd` attention) for certain benchmarking applications

**Collection**: NLP

# Usage
Data shuffling is automatically enabled.
To enable packed seq without `thd` attention, put the following in the run command
```bash
	+model.data.train_ds.packed_sequence=True 
	+model.data.train_ds.packed_sequence_return_cu_seqlen=False  # new
```

# Jenkins CI
To run Jenkins, a NeMo User with write access must comment `jenkins` on the PR.

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- [ ] 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

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# Additional Information
* Related to # (issue)
