This PR adds support for Advanced Custom Fields (ACF) in the generated OpenAPI specification, making ACF fields discoverable and properly typed in the API documentation.

It makes it significantly easier to work with ACF fields through the REST API, especially when using typed API clients or automated code generation tools.

• Automatic ACF detection: the plugin now automatically detects and includes ACF field schemas from WordPress REST API endpoints
• Improved type safety: ACF schemas are normalized to ensure proper typing, with special handling for complex field types like clone fields and flexible content layouts

The integration fetches ACF schema information directly from WordPress REST API OPTIONS requests and merges it into the OpenAPI specification. This means:

• ACF fields appear in the acf property of resources
• Type definitions are accurate and match WordPress's native schema
• Client code generators (like openapi-typescript and openapi-fetch) can create proper types for ACF fields
• API consumers get full documentation of available ACF fields

About the technical changes:

• Added new AddACFSchema filter class to handle schema augmentation
• Extended Operation class to support ACF schema in request bodies
• Integrated the new filter into the main schema generation flow