Release stabilised specification updates (2020-12 patch)

[Relequestual]

This work is encompassed by https://github.com/json-schema-org/json-schema-spec/milestone/9

This milestone is proposed by the patch release process community discussion. We didn't receive any strong objections so we will aim to deliver this process.

By default the due date is the expiration of the previous draft, but that date should not be taken too seriously unless ratified by the core team.

It's acknowledged that this milestones default due date was missed. Now aim for 2021 Q4.

I'll aim to nudge issues to being completed as much as possible.
I'll take responsibility for the release process.

Diff 2020-12 and current status of master branch.

The release process will be similar to #1040 (comment). This will likely be the last time we publish to the IETF (json-schema-org/community#69).

• Define proposed release process and copy steps to here
• First release candidate declared - 2 week review
• Add changelog
• Update any new ADRs to "accepted" status
• If required - Second release canddiate declared (may be skipped if no-one objects)
• Final review: Verify that the meta-schema and specification match
• Final review: Overall spelling, grammar, and wording consistency check
• Final review: Verify that all examples make sense and match current specs
• Final review: Verify that all notable changes are in the changelog section (For this release, see similar "fixes only" release changelog)
• Submit drafts to IETF (https://github.com/json-schema-org/json-schema-spec/wiki)
• Update the web site including release notes page (https://json-schema.org/specification.html)
• Announce on twitter / slack / open collective / google group mailing list
• Remove "master" branch from spec repo

[Relequestual]

Go team! Issue closed!