Define every `url` and `viewUrl` field as format `uri`

[davidB]

Changes

• define every fields url and viewUrl with format: "uri" as proposed in #191
• as the version of schema was with suffix -draft, I didn't update them

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]

Thanks @davidB - we discussed this topic during the last CDEvents WG and we plan to include it in the next milestone v0.5. We'll try to have most of the breaking changes in one milestone (v0.5). Once the v0.4 release is out (this week), this PR will have to be rebased and the version of the affected events updated.

[afrittoli]

@davidB - main is now open for v0.5 development - could you rebase your PR based on top of the updated main? @xibz @obowersa this PR is related to #162 and cleanup/consistency work we plan for v0.5.