GFM admonition blocks

[bric3]

Is your feature request related to a problem? Please describe.

Github now support admonition blocks

> [!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.

[!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.

Describe the solution you'd like

Ideally adding a new gfm extension to common-mark makes sense, to support this admonition syntax.

Describe alternatives you've considered

No alternative.

Additional context

Source [1], [2]