B2B-2677: [MediaGallery] Implement data caching for GraphQL results on resolver level

- Assert second store's cache record entry's label is null

Author: danmooney2

dev/tests/api-functional/testsuite/Magento/GraphQl/Catalog/ResolverCache/MediaGalleryTest.php

@@ -234,6 +234,9 @@ public function testResolverCacheRecordIsCreatedForEachStoreView()
             )
         );
 
+        // The entry's label in second store view is null by default; assert the cache record has the same value
+        $this->assertNull(json_decode($cacheEntryInSecondStoreView, true)[0]['label']);
+
         // Assert cache keys are different
         $this->assertNotEquals(
             $cacheKeyInDefaultStoreView,