Links Support

Add the ability to follow [OpenAPI 3 links](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#linkObject) to fetch additional data and add it to the response for a given operation. For example, you might get an item overview with a link to get item details. A new CLI option like `--link=details` could then be used to trigger the additional request and put a `details` field into the response with the response data from the details call. All of this would happen before response filtering/projection so you can select just the fields you care about.

Bonus: support an extension like `x-collection` so this works for calls that return a list of items, so that you can get the link for each item in the list by treating index 0 as a wildcard in the body pointer.

Start by reading the OpenAPI 3 Link Object specification linked in the issue, then trace the CLI option handling, additional request flow, and response filtering or projection entry points. Done means a named link such as `details` can trigger a follow-up request and add its response before projection; the optional `x-collection` behavior should handle list items via the proposed index-0 wildcard.

Scritto dal modello di indicizzazione a partire dal testo della issue.