Upgrade ajv

[mattcollier]

Currently, still using ajv@6 here and they are currently at 8. Thankfully, they are providing a nice upgrade guide:

https://github.com/ajv-validator/ajv/blob/master/docs/v6-to-v8-migration.md

The change list is long, and it's going to take some effort to assess the impacts of an upgrade.

https://github.com/ajv-validator/ajv/releases/tag/v8.0.0
https://github.com/ajv-validator/ajv/releases/tag/v7.0.0