Add samples for Invoice Template API

sample/invoice-templates/GetInvoiceTemplate.php

@@ -0,0 +1,31 @@
+<?php
+
+// # Retrieve Invoice Template Sample
+// This sample code demonstrate how you can get
+// an invoice template using templateId.
+
+use PayPal\Api\Template;
+
+$invoiceTemplate = require 'CreateInvoiceTemplate.php';
+
+/** @var Template $invoiceTemplate */
+$templateId = $invoiceTemplate->getTemplateId();
+
+// ### Retrieve Invoice Template
+// Retrieve the invoice template object by calling the
+// static `get` method
+// on the Template class by passing a valid
+// Template ID
+// (See bootstrap.php for more on `ApiContext`)
+try {
+    $template = Template::get($templateId, $apiContext);
+} catch (Exception $ex) {
+    // NOTE: PLEASE DO NOT USE RESULTPRINTER CLASS IN YOUR ORIGINAL CODE. FOR SAMPLE ONLY
+    ResultPrinter::printError("Get Invoice Template", "Template", $template->getTemplateId(), $templateId, $ex);
+    exit(1);
+}
+
+// NOTE: PLEASE DO NOT USE RESULTPRINTER CLASS IN YOUR ORIGINAL CODE. FOR SAMPLE ONLY
+ResultPrinter::printResult("Get Invoice Template", "Template", $template->getTemplateId(), $templateId, $template);
+
+return $template;