Add EventPrefix and EventObject to checkout agreement model

Author: yogesh-valiya

app/code/Magento/CheckoutAgreements/Model/Agreement.php

@@ -9,6 +9,16 @@
 
 class Agreement extends \Magento\Framework\Model\AbstractExtensibleModel implements AgreementInterface
 {
+    /**
+     * @var string
+     */
+    protected $_eventPrefix = 'sales_agreement';
+
+    /**
+     * @var string
+     */
+    protected $_eventObject = 'agreement';
+
     /**
      * Allowed CSS units for height field
      *