Add support for JSON Schema draft 2019-09 and 2020

[davidebriani]

JSON Schema draft 2019-09 has been out for a while and it's probably going to be quite common, given that OpenAPI 3.1 is also supporting it.
However support for this draft only comes with Ajv 7 and react-jsonschema-form is still stuck with Ajv 6.
Would you consider upgrading the package or maybe leave it as peer dependency?
Validation is a core part of this project and it makes sense to let users be able to stay up-to-date with current standards.

[heath-freenome]

@davidebriani rjsf-v5 will be adding support for ajv8. We can consider bumping the schema version support to the latest at that point.

[heath-freenome]

We are on Ajv8, but we still don't properly support some of the newer concepts in the latest drafts

[timruffles]

@heath-freenome do you have a link to something capturing the concepts/features not supported from 2019/2020?

[heath-freenome]

@timruffles alas, we do not at the moment. It is something that we definitely need to write up. And given that I (and others) are maintaining this project with the 2-4 hours a week of time our regular jobs and life allow us, it may take a while to generate. Sorry.

[timruffles]

All good, thanks for maintaining this!