Support generating values of type URL from JSON Schema

### Motivation

```
{
"time": "2023-12-06T20:45:17.385Z",
"url": "https://example.com"
}
```

For the above json data. The currently valid `openapi.yml` will use `string` to represent "time" and "url".

I'm hoping to somehow add support for URL and Date types directly on swift-openapi-generator.

### Proposed solution

1. Add a variant for OpenAPI 3.1 to allow "url" and "date" for type. (Not recommended)

2. ...

### Alternatives considered

None

### Additional information

_No response_

Start by reviewing how swift-openapi-generator maps OpenAPI 3.1 schemas to Swift types, focusing on the handling of string formats such as date and URL. The issue does not name files, tests, or a settled design; completion would require agreeing on the supported schema representation and validating generated Swift types for the example JSON values.

Written by the indexing model from the issue text.