Upgrade to Ajv 8

On top of these changes https://github.com/ajv-validator/ajv/blob/master/docs/v6-to-v8-migration.md I also saw that some of the validation error messages are changed.
i.e
```
      -    "message": "must match format \"abcName\""
      +    "message": "should match format \"abcName\""
```