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.

サンプルアプリケーションの Markdown レンダラーから始め、CommunityToolkit vNext と Labs にある既存の Experimental InfoBar を調査します。issue で参照されている GitHub と DocFX のアラート構文を比較し、その後、レンダラーと既存の Markdown で使用すべき形式を決定します。vNext から通知が削除され、両方のサンプルで一貫してレンダリングされ、関連する Labs と vNext の Markdown に選択したアラート構文が含まれていれば完了です。

索引モデルが issue の本文から書いたものです。