Support for chosen level in `PatchWSIDataset`

[bhashemian]

Is your feature request related to a problem? Please describe.
Following up on #3995, user likes to be able to define the whole slide image level when using PatchWSIDataset in order to load patches at that level.

Describe the solution you'd like
For the solution, we should consider that the location is always refer to the coordinates at level=0.