swift main signature changed due to support array result feature

Hi, dear openwhiskers. Then, all runtimes except ballerina image have supported `An action supports not only a JSON object but also a JSON array`, and supports sequence action as well. One important part is, only swift image's main signature has been changed from `func main(args: Any) -> Any

[discuss]Operation-invoker side-change prewarm container

Background # I think openwhisk needs some operation tools(page or API) to admin, for example: - real-time status of Action, Controller, Invoker, etc. - Change prewarm runtime container for invokers here, we just discuss