Add example App for Notice feature

Add an example app for the Notice feature.
https://argo-cd.readthedocs.io/en/latest/user-guide/application-notice/

Argo CD could also be configured to display a default banner on all App. Something like "Welcome to the official demo instance for the [Argo CD project](https://argoproj.github.io/cd/) 🎉 "

Start with the Notice feature documentation linked in the issue and inspect neighboring example apps in this repository to determine the expected structure. Add an example that demonstrates the Notice feature and the requested default banner behavior, then verify the example renders the notice as intended.

Written by the indexing model from the issue text.