Add support for multiple features in the middleware

[joelbutcher]

This PR add's multi-feature support to HasFeature middleware, using Laravel's comma-separated argument syntax when defining middleware on the route:

use App\Http\Controllers\FooController;
use RyanChandler\LaravelFeatureFlags\Middleware\HasFeature;

Route::get('foo', [FooController::class, 'index')->middleware(HasFeature::class, . ':foo,bar');

[ryangjchandler]

Thanks @joelbutcher!