Update API template to include metadata

What does this MR do?

The TW team has been adding stage / group ownership metadata to all pages in issues stemming from &3991 (closed). However, we can't edit api/graphql/reference/index.md directly, because the output is controlled by a script. So … we need to update the script that generates it.

cc to @cnorris because he's spearheading the metadata effort.

I'm sending this over to @cablett because she knows the ins and outs of dealing with the GraphQL API page. (She may also have feelings about what stage / group owns the page!) I'm not sure what steps I might need to take to get this MR through to completion, but dropping in what we need is the best start.

Related issues

Author's checklist (required)

• Follow the Documentation Guidelines and Style Guide.
• If you have Developer permissions or higher:
  • Ensure that the product tier badge is added to doc's h1.
  • Apply the documentation label, plus:
    • The corresponding DevOps stage and group labels, if applicable.
    • development guidelines when changing docs under doc/development/*, CONTRIBUTING.md, or README.md.
    • development guidelines and Documentation guidelines when changing docs under development/documentation/*.
    • development guidelines and Description templates (.gitlab/*) when creating/updating issue and MR description templates.
  • Assign the designated Technical Writer.

Do not add the feature, frontend, backend, ~"bug", or database labels if you are only updating documentation. These labels will cause the MR to be added to code verification QA issues.

When applicable:

• Update the permissions table.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Add the product tier badge accordingly.
• Add GitLab's version history note(s).
• Add/update the feature flag section.

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• Clear typos, like this is a typpo.
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