chore(docs): Updated API Reference (v2) (#9174)

Automated changes by [create-pull-request](https://github.com/peter-evans/create-pull-request) GitHub action

Co-authored-by: Oli Juhl <59018053+olivermrbl@users.noreply.github.com>

www/apps/api-reference/specs/admin/components/schemas/AdminPostExchangesAddItemsReqSchema.yaml

@@ -1,13 +1,13 @@
 type: object
-description: SUMMARY
+description: The details of outbound items.
 x-schemaName: AdminPostExchangesAddItemsReqSchema
 properties:
   items:
     type: array
-    description: The exchange's items.
+    description: The details of outbound items.
     items:
       type: object
-      description: The item's items.
+      description: An item's details.
       required:
         - variant_id
         - quantity
@@ -15,7 +15,7 @@ properties:
         variant_id:
           type: string
           title: variant_id
-          description: The item's variant id.
+          description: The ID of the associated product variant.
         quantity:
           type: number
           title: quantity
@@ -27,11 +27,11 @@ properties:
         internal_note:
           type: string
           title: internal_note
-          description: The item's internal note.
+          description: A note viewed only by admin users.
         allow_backorder:
           type: boolean
           title: allow_backorder
-          description: The item's allow backorder.
+          description: Whether the item can be added even if it's not in stock.
         metadata:
           type: object
-          description: The item's metadata.
+          description: The item's metadata, can hold custom key-value pairs.