z_downsampling metadata

[will-moore]

It's possible that we may generate multiple "datasets" for a given OME-Zarr Image, e.g. with and without down-sampling in Z. It could be useful to have a way to identify these.

See hms-dbmi/vizarr#71 (comment)
"will there be any way to distinguish between the downsampled-in-z version of a dataset and the non-downsampled version? The shape of the zarr array, I presume? But will there be any metadata about it? Just curious........."

@joshmoore "One thing we could do at the moment (pre-lightsheet changes) would be to have a naming convention for the multiscales themselves. Another option would be to use the metadata for the method of the downsampling, but we’d need something well-defined to say “in-z".

[will-moore]

oops - duplicate created since I got a 404 after trying to create the first time.