Allow `Schema.definitions` to be a file

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

I like to store a JSON file with the SCHEMA definition. It could be nice to be able to set definitions via:

 schema: {
  definitions: 'schema.json'
},

Feature / Enhancement Description

Allow setting a file to schema definitions

Example Use Case

 schema: {
  definitions: 'schema.json'
},

Alternatives / Workarounds

const definitions = await fs
    .readFile('spec/support/schema.json', 'utf8')
    .then(file => JSON.parse(file));
schema: {
  definitions
},

3rd Party References

Start by tracing how the schema configuration and its definitions entry are read, using the issue's schema.definitions example as the expected input. Check the existing schema-related tests or configuration entry points, then verify that a definitions path such as schema.json is loaded and parsed with the same behavior as inline definitions.