Add support for previewing MyST Enhanced Style

[psychemedia]

It would be useful if vscode-markdown-preview-enhanced could also render MyST notes and warnings style admonitions which take the form:

```{note}
Here is a note!
```

which is rendered by Jupyter Book, for example, as:

or

```{admonition} Here's your admonition
Here's the admonition content
```

which is likewise rendered as:

[adam-grant-hendry]

Please reference Issue #58 from the MyST-Markdown extension