image-label: JSON schemas and clarifications

[sbesson]

Fixes #125

This PR reviews the image-label specification and brings it inline with recent improvements made to other specifications including:

• the addition of JSON schemas, a minimal schema enforcing all MUST requirements and a strict schema enforcing all SHOULD requirements, together with tests
• the extraction of the embedded JSON snippets as standalone examples and their correction to be compliant with the schema
• an update to the specification paragraph to clarify the content and requirement levels of all keys defined by the specification

In addition to reviewing the validation tests keep passing and that the modified text is sensible, the two biggest changes that should be reviewed, notably by the original authors of the specification (all marked as reviewers of this PR) are:

• the current specification defines colors and properties keys with no requirement level and does not define the version key. In addiition to clarifying the expected content, this PR proposes a set of requirement levels using the keywords from RFC2119 and implemented through the JSON schemas
• the name of the JSON schema is initially set to strict_image-label.schema to follow the convention used for other JSON schemas while keeping the hyphen separator using in image-label. The mixture of underscore and hyphen is most likely confusing. Should we change to underscores? Update (2022-07-05): updated the proposal to use label.schema and strict_label.schema

[github-actions[bot]]

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[joshmoore]

Automated Review URLs

Argh. Again not working.

Otherwise, :+1: though I agree that the schema name is not particularly friendly.

[sbesson]

Otherwise, 👍 though I agree that the schema name is not particularly friendly.

Open to alternative suggestions but my concern is that this might force us to modify the name of existing published schemas - https://github.com/ome/ngff/tree/main/0.4/schemas.

[will-moore]

LGTM 👍

[sbesson]

Re the remaining sticking point (the name), considering simply naming the schemas as label.schema and strict_label.schema.

[will-moore]

Those names sound fine to me 👍

[joshmoore]

@sbesson : is it fair to say that this "fixes #125" as well?

[sbesson]

Yes and furthermore it only fixes #125. The previous description was erroneous (now updated)