Behavior: Creates multiple media builder items associated with the specified media builder ID. The media builder ID from the route is assigned to each input model before creation. Returns the change tracking results for all created items.

Authorization: Requires an authenticated user (class-level [Authorize]).

Side Effects: Multiple new media builder item records are persisted in the data store.

Error Scenarios: Returns 400 if the input array is null or contains invalid models. Returns 401 if the user is not authenticated.