Add support for GitLab fold tags "<summary>"

[PpChailley]

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Gitlab markdown supports a syntax for foldable sections with the code below.

Could you add support for this?

<details><summary>Section title</summary>
hidden text
</details>

References:

• https://docs.gitlab.com/ee/user/markdown.html#collapsible-section
• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/summary