Rename post-menu event

The post menu currently has a `toggleMenu` event (https://github.com/swisspost/design-system/blob/main/packages/components/src/components/post-menu/post-menu.tsx#L79C12-L79C22). This event should be renamed to `postToggle`. 

- [ ] Rename the event in the post-menu
- [ ] Rename the event in all listeners 