Update GraphQL docs tooling for Hugo site launch

What does this MR do and why?

Updates docs templates for the GraphQL reference page to work with the new Hugo docs website.

The new site uses shortcodes for custom markdown elements, so we need to update formatting for details, alerts, and SVG icons.

Here's the page in the review app for this MR: https://new.docs.gitlab.com/upstream-review-mr-ee-178795/api/graphql/reference/

Do not merge until Hugo site launch, Feb 16-17.

References

gitlab-org/technical-writing/docs-gitlab-com#168 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.