Schema development: main or branch, in parallel or at release time?

[handrews]

I'm splitting out the schema-related concerns from #3677 as we decided in a recent TDC meeting that the schema, spec, and gh-pages parts have different priorities (and probably involve different people).

• New schemas are created for each minor or major release
  • Patch releases are limited to changes that would not require a separate schema for each patch release in a minor release line
  • Should new minor/major schemas be created and updated in parallel with spec changes, or deferred and created all at once just prior to the release, as part of the final review effort?
  • If created and updated in parallel, this should be integrated with the development branch process being sorted out in Define and document branch strategy for the spec, both development and publishing #3677, presumably continuing to be published to main in the current schemas/, just as Define and document branch strategy for the spec, both development and publishing #3677 recommends publishing the markdown to the current versions/ location
• Schemas can currently also be changed for bug-fixing or functional improvement at any time, and released independently from the release schedule (see also Define and document our schema publishing process #3715)
  • This includes but is not limited to patch release-related bug fixes
  • This might require a different tagging strategy from whatever we do for spec releases