docs: add standalone-prices to list of reserved words (#2756)

Author: kark

website/src/content/api-reference/application-config.mdx

@@ -160,8 +160,9 @@ Some values are reserved for internal usage and cannot be used:
 * `settings`
 * `welcome`
 * `disabled`
+* `standalone-prices`
 
-Note that the list can be extended at any time. _Last update 2022-01-01_.
+Note that the list can be extended at any time. _Last update 2022-08-11_.
 
 </Warning>