Implement Markdown Rendering Support for Notes, Warnings, and Info in Sample App

## Background
The sample applications for both CommunityToolkit vNext and CommunityToolkit Labs currently utilize an "Experimental" InfoBar with "Informational" severity.

## Problem
The aforementioned notice is exclusively applicable to Labs components and is not removable in the Toolkit vNext sample app.

## Solution
- [ ] Remove the notice from the sample app.
- [ ] Integrate the notice as a feature of the markdown renderer within the sample app. This will allow for better rendering of documents that contain elements like `![NOTE] Some information`, which currently do not render as expected.
- [ ] Update existing markdown in Labs and Toolkit vNext to include the experimental InfoBar. We'll remove them from vNext when we launch stable.

This change will enhance the readability of our documentation and ensure consistent user experience across both CommunityToolkit vNext and CommunityToolkit Labs.

## Open questions
Both DocFX and GitHub have their own syntax for this.
- GitHub: https://github.com/orgs/community/discussions/16925
- DocFX: https://dotnet.github.io/docfx/docs/markdown.html?tabs=linux%2Cdotnet#alerts

Which one do we want to use?
- If we use **GitHub** syntax, it will display on GitHub correctly, but need to be transformed to the DocFX format when we add support for that.
- If we use **DocFX** syntax, it won't need to be transformed before being built for DocFX, but it also won't show up right on GitHub.

Beginne mit dem Markdown-Renderer der Beispielanwendungen und untersuche die bestehende Experimental InfoBar in CommunityToolkit vNext und Labs. Vergleiche die in der Issue referenzierten GitHub- und DocFX-Alert-Syntaxen und entscheide dann, welches Format der Renderer und das bestehende Markdown verwenden sollten. Als erledigt gilt die Aufgabe, wenn der Hinweis aus vNext entfernt wurde, in beiden Beispielen konsistent gerendert wird und das relevante Labs- und vNext-Markdown die gewählte Alert-Syntax enthält.

Vom Indexierungsmodell aus dem Issue-Text verfasst.