scripts: add scale.py

[joshmoore]

Simple script to enable downsampling a Zarr array.

[joshmoore]

Updated the script to safely transfer labeled images (according to the current set of open PRs):

(cv) /opt/ebi-repo/6001247.zarr/labels /opt/omero-ms-zarr/src/scripts/scale.py --method=nearest 0 1 --labeled --copy-metadata
level 0 (1, 1, 257, 210, 253) = 49 labels
level 1 (1, 1, 257, 126, 105) 49
level 2 (1, 1, 257, 52, 63) 49
level 3 (1, 1, 257, 31, 26) 49
level 4 (1, 1, 257, 13, 15) 49
copying attribute keys: ['color', 'image']

I'll likely move forward with getting these on S3 for testing.

cc: @erindiel

[joshmoore]

Closing in favor of ome/ome-zarr-py#45

cc: @erindiel