Add 'Search' to API

Add the search function to the API as it is missing from the documentation

Author: artistro08

src/PrintfulProducts.php

@@ -47,6 +47,7 @@ public function __construct(PrintfulApiClient $printfulClient)
     public function getProducts($offset = 0, $limit = 20)
     {
         $requestData = [
+            'search' => (string)$search,
             'offset' => (int)$offset,
             'limit' => (int)$limit,
         ];