Add an optional schemaUri to the context

[afrittoli]

Changes

Add schemaURI to the context. It can be used to link to a custom schema that further refines the event content.

Context:

• https://github.com/cdevents/spec/issues/168
• https://github.com/cdevents/spec/issues/91

Also fixes a small issue in the event-version.sh tool that prevented example versions from being updated.

Fixes: #91

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• [x] Has the primer doc been updated if a design decision is involved
• [x] Have the JSON schemas been updated if the specification changed
• [x] Has spec version and event versions been updated according to the versioning policy
• [x] Meets the CDEvents contributor standards

[afrittoli]

This looks mostly good to me.

But, regarding the capitalized 'URI' in this proposal - I see that we have noted it differently on e.g. viewUrl here: https://github.com/cdevents/spec/blob/main/schemas/repositorycreated.json#L74 We also have an old (forgotten?) action to capitalize words such as URI from https://hackmd.io/2FRGlw9fTMmKN1OQUVvguA?view#Jan-29-2024. What is the best to do?

• Update this PR to instead define schemaUri?
• Update all existing occurrences of Uri/Url to URI/URL?
• Keep this PR as-is, but create a dedicated issue to deal with the inconsistencies separately?

The issue was initially brought up in Dec 2023 https://github.com/cdevents/community/blob/main/working-group-notes-2023.md#dec-4-2023. There are different opinions about this on the internet, but I don't think there is a definite answer out there. One point that I found relatively compelling is that two acronyms next to each other become indistinguishable if their case is all upper.

I will update this PR to use Uri instead of URI to be consistent with viewUrl - we can then open a separate issue if anyone feels strongly that this should be all uppercase instead