Add vue 3 sample app for example purpose

[GaetanWi]

Hello,

As mentioned on Discord, please find attached a PR in order to serve a Vue 3 App.

[michaelbromley]

Hi!

Thanks for the contribution. I just testing this locally and it works fine and wow - vue 3 compiles very fast!

One thing I'd like to see is that the vue3 app demonstrates how to interact with the host Admin UI app, like you see in the existing Vue and the React examples - i.e. fetch a list, make a mutation, and display a notification.

If that is something you would consider adding, I think it would make the demo even more useful for helping people get started with Vue 3 extensions. Let me know :)

[GaetanWi]

I'll try to take a look at this as soon as I can !