[sparsity] Base sparsity level scheduler class (#59770)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59770
Implements the base scheduler class for changing the sparsity levels in the sparsifier.
Test Plan:
```
python test/test_ao_sparsity.py
```
Imported from OSS
Differential Revision:
D29070603
D29070603
Reviewed By: raghuramank100
Pulled By: z-a-f
fbshipit-source-id: 0b160e4eb0a2a303d2d19e6a3beb4784002b2cb7
