docs: change from detecting version to since tag (#13127)

* update everything from version to since

* update events

* regenerate oas

www/apps/api-reference/specs/store/paths/store_carts_{id}_customer.yaml

@@ -87,4 +87,4 @@ post:
         ```
       description: Emitted when the customer in the cart is transferred.
       deprecated: false
-      version: 2.8.0
+      since: 2.8.0

www/apps/api-reference/specs/store/paths/store_returns.yaml

@@ -67,4 +67,4 @@ post:
         ```
       description: Emitted when a return is marked as received.
       deprecated: false
-  x-version: 2.8.0
+  x-since: 2.8.0