refactor: move setFilter to Resource class

[Regaez]

Perhaps the setFilter function could be moved into the abstract Resource class and made to be generic, so it's not repeatedly defined in all the different resource types, e.g.

protected function setFilter()
{
    $filter = Config::instance()->{$this->getResourceType()}->get->fields;
    
    if (!empty($filter)) {
        $this->filter = $filter;
    }
}

Then would need to adjust mapping so that getResourceType() returns the correct value for the config... currently would return user not users etc