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