[ao][sparsity] Added the Nearly Diagonal Sparsifier
This sparsifier creates a nearly diagonal mask to be applied to the weight matrix.
Nearly Diagonal Matrix is a matrix that contains non-zero elements near the diagonal and the rest are zero.
An example of a nearly diagonal matrix with degree (or nearliness) 3 and 5 are follows respectively.
1 1 0 0 1 1 1 0
1 1 1 0 1 1 1 1
0 1 1 1 1 1 1 1
0 0 1 1 0 1 1 1
Note that a nearly diagonal matrix with degree 1 is just a matrix with main diagonal populated
This sparsifier is controlled by one variable:
1. `nearliness` defines the number of non-zero diagonal lines that are closest to the main diagonal.
Currently - supports only odd number
Note:
This can be accelerated (vectorized) once the Spdiagonal feature (PR: #78439) is landed or the banded matrix
feature is landed: https://stackoverflow.com/questions/52463972/generating-banded-matrices-using-numpy
Test Plan:
```
python test/test_ao_sparsity.py TestNearlyDiagonalSparsifier
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78448
Approved by: https://github.com/z-a-f, https://github.com/HDCharles
