Add support for Obsidian type blockquote alerts

[bep]

• Make the alert type parsing more flexible to support more types
• Add AlertTitle and AlertSign (for folding)

Note that GitHub will not render callouts with alert title/sign.

See https://help.obsidian.md/Editing+and+formatting/Callouts

Closes #12805
Closes #12801

[jmooring]

I created a render hook to handle blockquotes with and without an alert title:

layouts/_default/_markup/render-blockquote.html

{{ $emojis := dict
  "caution" ":exclamation:"
  "important" ":information_source:"
  "note" ":information_source:"
  "tip" ":bulb:"
  "warning" ":information_source:"
  "danger" ":radioactive:"
}}

{{ if eq .Type "alert" }}
  <blockquote class="alert alert-{{ .AlertType }}">
    <p class="alert-heading">
      {{ transform.Emojify (index $emojis .AlertType) }}
      {{ with .AlertTitle }}
        {{ . }}
      {{ else }}
        {{ or (i18n .AlertType) (title .AlertType) }}
      {{ end }}
    </p>
    {{ .Text  }}
  </blockquote>
{{ else }}
  <blockquote>
    {{ .Text }}
  </blockquote>
{{ end }}

Then I tested this Mardown:

> [!danger]
> Do not approach or handle without protective gear.

---

> [!danger] Radiation hazard
> Do not approach or handle without protective gear.

The above was rendered to:

In the first example AlertTitle is the same as AlertText. I expected to see this instead:

[bep]

@jmooring thanks, I have force pushed a fix.

[jmooring]

This looks good to me.