add ability to pass a closures to ResourceRelationshipGuesser

[jerothor]

I would like to be able to pass my own closure to ResourceRelationshipGuesser

because I like appending Resource to my resource classes so its easier to differentiate between models.

for example, in nova service provider:

Nova::$guessResourceUsing = function ($name) {
    return '\\App\\Nova\\' . $name . 'Resource';
}

ResourceRelationshipGuesser class:

class ResourceRelationshipGuesser
{
    public static function guessRelation($name)
    {
        if (Nova::$guessRelationUsing) {
                return Nova::$guessRelationUsing($name);
        }

        return Str::camel(str_replace(' ', '_', $name));
    }

    public static function guessResource($name)
    {
        if (Nova::$guessResourceUsing) {
                return Nova::$guessResourceUsing($name);
        }

        $singular = Str::studly(Str::singular($name));

        if (class_exists($appResource = Application::getInstance()->getNamespace().'Nova\\'.$singular)) {
            return $appResource;
        }

        $results = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 4);

        return str_replace(
            class_basename($results[3]['class']),
            $singular,
            $results[3]['class']
        );
    }
}

thank you for your consideration.