Feature: Announcement Banners

[yousinix]

We want a way to announce big releases/updates all over the docs.
Similar to the "🎉️ Docusaurus v3.5 is out! 🥳️" banner below.

🔗 Preview

[Ehesp]

Ah interesting... Do you want these fixed or closable? Also that's pretty big in size for docs, so a smaller header one sounds like a good idea

[yousinix]

I realize that the original issue might be a bit ambiguous because there are two banners with the same text. I originally meant the small banner on top, which is not that big as the other one.

It will be a good idea to have it dismissable, otherwise it can be visually annoying.
Our use case would to be to announce the public beta release of Widgetbook Cloud.

[Ehesp]

Ok I've had a look how Docusarus do this, and the ID of the banner is stored in local storage and checked client side. Makes sense, I just need to check how to deal with potential layout shift with this rendering on the client.