Downsample scale option

[will-moore]

For an Image of C:3, Z:10, Y:1024, X: 1024 you may wish to NOT downsample in Z when exporting. Only downsample in X and Y, e.g.

omero zarr export Image:123 --ds_scale 1,1,2,2

Whereas if you have an image with C:3, Z:1024, Y:1024, X: 1024 you may wish to downsample in Z, e.g.

omero zarr export Image:123 --ds_scale 1,2,2,2

This option gives complete flexibility over downsampling of all dimensions. Too complex?

Compare with ngff-zarr which has

scale_factors : int of minimum length, int per scale or dict of spatial dimension int's per scale
        If a single integer, scale factors in spatial dimensions will be increased by a factor of two until this minimum length is reached.
        If a list, integer scale factors to apply uniformly across all spatial dimensions or
        along individual spatial dimensions.
        Examples: 64 or [2, 4] or [{'x': 2, 'y': 4 }, {'x': 5, 'y': 10}]

at https://github.com/thewtex/ngff-zarr/blob/4a154994a85e2d222999bb3e5d67ab96f5060244/ngff_zarr/to_multiscales.py#L219