units instead of unit

[will-moore]

As reported scalableminds/webknossos#6577 (comment)
some of our sample data uses "units" for v0.4 axes
when the spec says "unit": https://ngff.openmicroscopy.org/latest/#axes-md

Checking the ngff repo I see that the schema uses "units":

ngff/0.4/schemas/image.schema

Line 127 in 0a087b8

"units": {

whereas the example files use "unit"
https://github.com/ome/ngff/blob/main/0.4/examples/multiscales_strict/multiscales_example.json
and some of the test files use both! https://github.com/ome/ngff/blob/0a087b8319b234a0682bc4853e390314f76f7540/0.4/tests/strict_image_suite.json

I guess the issue here is that having "unit" when the schema states "units" is not actually invalid, as the schema allows unknown keys to be added.

[sbesson]

Looking at the history of 0.4 and especially #57, I suspect the confusion comes from the fact that the initial implementation had a field called units and this got transformed into unit (specifically in 70ebede).

Although an units field is not invalid per se, the specification uses unit and I think our examples, our validation and generation tools should exclusively use this terminology. Related to the example above, I see a few places that should be updated:

1. the JSON schemas & the associated JSON test files
2. the omero-cli-zarr generation tool - see https://github.com/ome/omero-cli-zarr/blob/9cce537d049531e565a6a9eec77498f82c97a0c0/src/omero_zarr/util.py#L47-L51
3. the representative examples (probably generated by the tool above)