[ao][sparsity] Training-aware data sparsity callback for lightning (#80371)
This callback aims to sparsify the model inside lightning module after training.
**Note that the model is copied and then sparsified, so the existing model is not modified**
The sparsified model can be used for comparison and can be accessed using
<callback_obj>.sparsified
Test Plan:
```python torch/ao/sparsity/_experimental/data_sparsifier/lightning/tests/test_callbacks.py TestTrainingAwareCallback```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80371
Approved by: https://github.com/z-a-f
