[node-core-library] Implement json-schema 'draft-07' validation

[bartvandenende-wm]

Summary

[node-core-library] Implements json-schema 'draft-07' validation in JsonFile / JsonSchema

Fixes https://github.com/microsoft/rushstack/issues/4713

Details

This PR:

• Upgrades 'ajv' from v6.x to v8.x in the rush repo
  • see for more information https://ajv.js.org/v6-to-v8-migration.html
• Replaces the 'z-schema' library with 'ajv' in @rushstack/node-core-library
  • This migration is required to be able to properly support json-schema draft-07 (and other future specifications), z-schema does not see very active development anymore.
  • Updates the schema validator error-detail helper to error details exposed by ajv
    • Since ajv uses a slightly different error message format, there are a couple of small breaking changes in downstream project that have test assertions on them.
  • Use 'ajv-draft-04' to retain backwards compatibility with json-schema draft-04
    • see https://ajv.js.org/guide/schema-language.html#draft-04
  • ajv applies additional validation on the correctness of the schema per https://ajv.js.org/options.html#strictschema
    • this surfaced a small issue in the heft schema validation where 'items' keyword was incorrectly combined with the string type.

Notes:

• Schema definitions that don't have a schema defined will now default to draft-07.
• There are likely some performance gains with the migration from 'z-schema' to 'ajv' that where not quantified, more background https://ajv.js.org/guide/why-ajv.html#super-fast-secure.

How it was tested

1. validated the existing unit tests and updated the new error detail snapshot
2. added new unit test to specifically test draft-04, draft-07 and nested schemas

Impacted documentation

N/A