v3.0.4 schema updates

[karenetheridge]

Brings the schemas up to date for the v3.0.4 release (see #4125), and adds some support scripts which are used to check for validation errors and inconsistencies between the yaml and json versions of the files.

$ json-schema-eval --validate-schema schemas/v3.0/schema.json
{
  "valid": true
}

$ scripts/compare schemas/v3.0/schema
schemas/v3.0/schema.yaml and schemas/v3.0/schema.json are identical.

[karenetheridge]

Why don't we just generate it [the JSON file] for publication in the gh-pages branch?

I don't object to that if it wouldn't inconvenience contributors or tool vendors. It's not difficult to convert the yaml file in main (or a topic branch) to json on the fly, but the barrier is not zero.

[handrews]

@karenetheridge we already have a YAML-to-JSON script that was run every time we published, as changes were (and are) _only_committed directly to the YAML version. So this isn't a new thing. The only baffling thing to me is why we ever checked the JSON in to main. We have, AFAICT, never used it for anything as it was regenerated on each publication. All it does is confuse people into thinking they need to keep it in sync on main.

[ralfhandl]

Converted to draft as it needs to be adjusted after merging

• #4146