Ajv6 is past EOL, upgrade AJV

[newt10]

AJV@6 was EOL on 30 June 2021. We should start looking at upgrading AJV since it is an essential piece that makes this library work.

Ajv is already one of the most performant json schema validators so I am proposing that we continue using AJV and take a step by step approach to upgrading.

1. Upgrade to latest version of AJV@7
2. Start a beta branch where more folks from community can try, test and provide feedback.
3. Create a new version with breaking changes

Prerequisites

• I have read the documentation;
• In the case of a bug report, I understand that providing a SSCCE example is tremendously useful to the maintainers.
• Ideally, I'm providing a sample JSFiddle or a shared playground link demonstrating the issue.

[newt10]

@epicfaace what do you think about this? I have a PR where I have been able to integrate ajv@7 into the library in the linked PR.

I would like to include this in 4.x

[heath-freenome]

RJSF v5 Beta has decoupled AJV from the core implementation and provides both an AJV6 and AJV8 implementation... Closing