Fix: Add missing duration attribute to webhook-request-log model

The duration field was being returned by the API but wasn't defined
in the Ember Data model, causing it to be undefined.

Added: @attr('number') duration;

This will fix the webhook response time chart showing 0.000ms.

Author: roncodes

addon/models/webhook-request-log.js

@@ -19,6 +19,7 @@ export default class WebhookRequestLogModel extends Model {
     @attr('string') reason_phrase;
     @attr('string') url;
     @attr('number') attempt;
+    @attr('number') duration;
     @attr('raw') response;
     @attr('raw') headers;
     @attr('raw') meta;