Support creating subsets via napari

[berombau]

Remote large dataset viewing is nice, but creating subsets is nicer. We can do this manual with number and plotting the subset, but drawing squares in napari is nicer.

This is similar to https://spatialdata.scverse.org/en/latest/tutorials/notebooks/notebooks/examples/napari_rois.html. It does not need to be a seperate widget, just a notebook with documentation.