Added billing webhooks and sorted trigger list

Author: clairekinde11

src/content/docs/integrate/webhooks/add-manage-webhooks.mdx

@@ -73,25 +73,43 @@ Events can also be retrieved using:
 
 ## Webhook triggers
 
-Available triggers include:
+### Authentication webhooks
 
 ```jsx
 organization.created;
-organization.updated;
 user.created;
-user.updated;
-user.deleted;
 user.authentication_failed;
 user.authenticated;
-organization.deleted;
+subscriber.created;
+access_request.created;
+```
+
+### User management webhooks
+
+```jsx
 role.created;
 role.updated;
 role.deleted;
 permission.created;
 permission.updated;
 permission.deleted;
-subscriber.created;
-access_request.created;
+organization.updated;
+organization.deleted;
+user.updated;
+user.deleted;
+```
+
+### Billing webhooks
+
+```jsx
+customer.agreement_cancelled;
+customer.agreement_created;
+customer.invoice_overdue;
+customer.meter_usage_updated;
+customer.payment_failed;
+customer.payment_succeeded;
+customer.plan_assigned;
+customer.plan_changed;
 ```
 
 <Aside>