Add JSON exception rendering helper for API routes

[LucasCavalheri]

This PR adds a small DX improvement for API-first Laravel applications.

It introduces a new convenience method:

$exceptions->shouldRenderJsonForApiRoutes();

which internally configures exception rendering for api/* routes using the existing shouldRenderJsonWhen(...) API.

The install:api command/stubs have also been updated to automatically enable JSON exception rendering for API routes in newly generated applications.

This helps avoid a common source of confusion when testing API routes with tools such as Postman, Insomnia, or curl without manually sending the Accept: application/json header.

The implementation is intentionally minimal and does not mutate the incoming request or alter existing expectsJson() behavior.