Add elk layout support to mermaid (#36486)

Fixes: https://github.com/go-gitea/gitea/issues/34769

This allows the user to opt-in to using `elk` layouts using either YAML
frontmatter or `%%{ init` directives inside the markup code block. The
default layout is not changed.

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

package.json

@@ -15,6 +15,7 @@
     "@github/relative-time-element": "5.0.0",
     "@github/text-expander-element": "2.9.4",
     "@mcaptcha/vanilla-glue": "0.1.0-alpha-3",
+    "@mermaid-js/layout-elk": "0.2.0",
     "@primer/octicons": "19.21.2",
     "@resvg/resvg-wasm": "2.6.2",
     "@silverwind/vue3-calendar-heatmap": "2.1.1",