postsaveurl() plugin type is called after an item in the outbox is saved. If
backgroundSync is true, the plugin is executed immediately on submit. Otherwise, @wq/app will wait for a response from the server before calling the plugin. The URL (or redux action) returned from the function will be used to determine the next navigation state.
postsaveurl() behavior in @wq/app is to navigate to the list view (if
backgroundSync is true) or to the detail view for the newly saved item (if
backgroundSync is false).