Improve callout shortcode. (#31802)

Remove the `markdownify` call, and instead rely on Hugo's proper syntax; `{{% callout %}}` when we want to the content to be processed as Markdown.

This allows for stuff like:

{{% callout info %}}
##### I'm an info callout!

```css
.foo {
  color: #fff;
}
```

{{< example >}}
<div class="alert alert-warning alert-dismissible fade show" role="alert">
  <strong>Holy guacamole!</strong> You should check in on some of those fields below.
  <button type="button" class="btn-close" data-dismiss="alert" aria-label="Close"></button>
</div>
{{< /example >}}
{{% /callout %}}

site/content/docs/5.0/components/card.md

@@ -386,9 +386,9 @@ Turn an image into a card background and overlay your card's text. Depending on
 </div>
 {{< /example >}}
 
-{{< callout info >}}
+{{% callout info %}}
 Note that content should not be larger than the height of the image. If content is larger than the image the content will be displayed outside the image.
-{{< /callout >}}
+{{% /callout %}}
 
 ## Horizontal
 
@@ -433,9 +433,9 @@ Use [text and background utilities]({{< docsref "/utilities/colors" >}}) to chan
 {{< /card.inline >}}
 {{< /example >}}
 
-{{< callout info >}}
+{{% callout info %}}
 {{< partial "callout-warning-color-assistive-technologies.md" >}}
-{{< /callout >}}
+{{% /callout %}}
 
 ### Border