Allow OrderController::index(...) in routes

[reindert-vetter]

Since php 8.1 we can do the following in routes/api.php:

Route::get('orders', OrderController::index(...));

This already works in its simplest form.

What doesn't work yet:

• Dependency Injection
• When caching the routes we should serialize the callback using the laravel/serializable-closure package (and test performance).

I would like to solve these 2 issues. Can you think of any other issues?