Update docs for new `MODULE_DOM_UPDATED` notification

Add the docs for the new notification ([Discussion](https://github.com/MagicMirrorOrg/MagicMirror/issues/3534) | [PR1](https://github.com/MagicMirrorOrg/MagicMirror/pull/3535) | [PR2](https://github.com/MagicMirrorOrg/MagicMirror/pull/3548))

1. Update notifications page with new notification
2. Update the `updateDom` section to mention this notification