Prefix event names in StoryLive

[Gazler]

As it stands, StoryLive has the following handle_event function clauses:

              def handle_event("set-theme", %{"theme" => theme}, socket)
              def handle_event("set-tab", %{"tab" => tab}, socket)
              def handle_event("set-tab", %{"navigation" => %{"tab" => tab}}, socket)
              def handle_event("clear-playground-error", _, socket)
              def handle_event("assign", assign_params, socket = %{assigns: assigns})
              def handle_event("toggle", assign_params, socket = %{assigns: assigns})

It is possible for a name collision with an event coming from a component rendered in the story (especially toggle). Perhaps these events should be prefixed to prevent weird issues with events coming from components.