What issue does this pull request resolve?

This PR addresses draft-04 compatibility gaps impacting OpenAPI example validation for OAS 3.0 and earlier (including 2.0). It is related to the CLI issue: Redocly/redocly-cli#1610

What changes did you make?

• Added support for JSON Schema draft-04 to improve validation of OpenAPI example(s) in specs that rely on draft-04-era semantics (OAS 3.0 and below).
• The implementation is based on the official Ajv draft-04 package approach and code structure: https://github.com/ajv-validator/ajv-draft-04/tree/master
• Wired draft-04 meta-schema / vocabulary handling so draft-04 schemas can be compiled and validated correctly in this fork.

Is there anything that requires more attention while reviewing?

• Meta-schema switching: draft-04 and later drafts (e.g., 2019-09 / 2020-12) use different vocabularies/keywords, so you cannot safely “switch” the meta-schema within a single Ajv instance and expect consistent behavior. Mixing drafts in one instance can lead to keyword/vocabulary conflicts and incorrect validation.
  Recommended approach is to keep draft-04 support isolated

Related prs:

• ajv: feat: add handling for draft-04 style for boolean in exclusiveMinimum and exclusiveMaximum #30
• cli: TBD