fix(retail): add region tag for JS - Update get-product.js (GoogleCloudPlatform#4113)

* Update search-simple-query.js

Added region tag to simply search query for code snippet update in the documentation.

* Update search-with-pagination.js

* Update get-product.js

Author: rebeccaellis

retail/interactive-tutorials/product/get-product.js

@@ -11,7 +11,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-
+// [START retail_get_product]
 'use strict';
 
 async function main(generatedProductId) {
@@ -60,3 +60,4 @@ process.on('unhandledRejection', err => {
 });
 
 main(...process.argv.slice(2));
+// [END retail_get_product]