schemaValidation - Improved OpenAPI to JSON schema conversion

[thim81]

linked to #642 #494

• Improved OpenAPI to JSON schema conversion to handle OpenAPI-specific properties in correct format
• strip unneeded OpenAPI-specific properties ('discriminator', 'readOnly', 'writeOnly', 'xml', 'externalDocs', 'example','deprecated') for more compact JSON schemas.
• Added JSON schema validation warning during conversion, to inform the users.

We don't stop the Portman conversion but skip the JSON Validation injection in Postman, like we did in the past for $ref properties.

This PR also solves a long lasting issue, where the openapi-to-postman converter injected/modified unwanted properties (minItems, maxItems).

CONVERSION WARNING

SKIP JSON Validation injection

BEFORE

AFTER

The test snapshot are changed because of the stripping of the unneeded OpenAPI-specific properties.

[thim81]

@nicklloyd I kept a range of test but skipped them (it.skip) to be removed after we got confirmation from the community/users.

[savage-alex]

Thanks @thim81 looking forward to it