Validate `$ref` in OpenAPI Schema

[ankitk-me]

Is your feature request related to a problem? Please describe.
In OpenAPI specifications, $ref fields like $ref: "#/components/schemas/Pet" can cause inconsistent behavior in Zilla if they are incorrectly written due to typos or mistakes.

Describe the solution you'd like
Add validation logic that checks all $ref values in the OpenAPI document to ensure they resolve to valid paths. And log events for invalid $ref.