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/openapi.full.yaml

@@ -1360,7 +1360,7 @@ paths:
             ```
           description: Emitted when the customer in the cart is transferred.
           deprecated: false
-          version: 2.8.0
+          since: 2.8.0
   /store/carts/{id}/gift-cards:
     post:
       operationId: PostCartsIdGiftCards
@@ -8845,7 +8845,7 @@ paths:
             ```
           description: Emitted when a return is marked as received.
           deprecated: false
-      x-version: 2.8.0
+      x-since: 2.8.0
   /store/shipping-options:
     get:
       operationId: GetShippingOptions