Feature Request: Add support for rendering GitHub blockquote highlight/alert ("Note", "Warning", etc)

[brainwo]

This is a new feature added in GitHub. More information can be found in this GitHub community discussion page.

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Example of all alert available:

[!NOTE]
Highlights information that users should take into account, even when skimming.

[!TIP] Optional information to help a user be more successful.

[!IMPORTANT]
Crucial information necessary for users to succeed.

[!WARNING]
Critical content demanding immediate user attention due to potential risks.

[!CAUTION] Negative potential consequences of an action.

[brainwo]

Related: #618

Admonitions support similar alert type with additional support for nesting. However this isn't supported by the GitHub Flavored Markdown Spec.