Support loading data from a specific resolution of a .zarr pyramid

[talonchandler]

@dsundarraman and I are planning to bring multiscale pyramids to the course so that we can iterate quickly on downsampled versions of our data.

@mattersoflight and I think it would be useful to add a resolution parameter to HCSDataModule. Default resolution=0 would load from the highest resolution, and larger integers would pull from lower resolutions of the pyramid.

What do you think @ziw-liu? I will have an example store to test with soon.

[mattersoflight]

Please also consider how we can concatenate multiple datasets at specific resolutions (see this dataloader) for training.

[ziw-liu]

#195 also implements support for this.