Add the ability to inject Views into Markdown articles

[jverkoey]

Consider a markdown article like this:

Lots of text

<div class="flex flex-row items-center justify-center flex-wrap">
  Some HTML.
</div>

Lots more text.

The div portion of the Markdown would ideally be injectable in some fashion using a more canonical Slipstream View definition:

var body: some View {
  Div {
  ...
  }
}

This would require some kind of special markup that the Markdown renderer would need to handle.