Add ability to append Nova filters to resource tests

[amiranagram]

This PR adds an ability to append Nova filters to getResource requests.
It reveals withFilter method that can be chained easily in tests.

Example:

use App\Nova\Filters\UserRoleFilter;

$this->modelClass::factory(10)->create();

$this
    ->withFilter(UserRoleFilter::class, 'admin')
    ->getResources();

As an array:

use App\Nova\Filters\UserRoleFilter;
use App\Nova\Filters\UserStatusFilter;

$this->modelClass::factory(10)->create();

$this
    ->withFilter([
        UserRoleFilter::class => 'admin',
        UserStatusFilter::class => 'active',
    ])
    ->getResources();