change schema draft to draft2020-12

[tonyfast]

this pull request points the schema to https://json-schema.org/draft/2020-12/schema.
we need to bump the schema to at least Draft2019 to gain the deprecation semantics.
yesterday in the schema meeting we decided that we should be using to the most current draft to get the most out of json schema.

[agoose77]

@filipsch in #1 (comment) you noted that your meeting schedules are very full at the moment. I don't want to put undue pressure on your time if it's no longer viable for you. I just wanted to check that you're still interested in shepherding this proposal. Are you still happy to be involved here?

If you are still keen, I think we all should work out a policy/process for how we collaborate on this JEP (in this repo), so that you and others who can't make the weekly meeting can contribute on a schedule that works for you. We already have challenges getting everyone in the meeting due to timezones and availability.

I also think it would be helpful to add additional maintainers, so that the bus factor is reduced. Let me know if you'd be happy to add some additional people.

I am thinking that we don't need to formalise too much here w.r.t contributing, but we probably want to open PRs that allow everyone to weigh in. We could say e.g. PRs should be left open for a couple of days to allow people to comment, but that would slow things down if the PRs are tiny.

I mainly want us to make it possible to satisfy the following objectives:

• Allow async and remote contributors
• Keep momentum up!

@tonyfast do you have any feelings here?

[filipsch]

@agoose77

• Just added all the authors of the JEP as collaborators, so I'm no longer the blocker here. Thanks for suggestion
• I'm happy to leave the shepherding over to you.