Add server variables support to OpenAPI spec

Max Woolfrequested to merge
586604-custom-hostname-openapi3 into master

What does this MR do and why?

  • This change makes GitLab's OpenAPI documentation more flexible by allowing it to work with different GitLab installations, not just gitlab.com.

  • Previously, the API documentation was hardcoded to only point to "https://gitlab.com/api". Now it uses a template format "https://{hostname}/api" where the hostname can be customized. This means organizations running their own private GitLab servers can use the same API documentation by simply changing the hostname variable to match their server's address. This retains gitlab.com as the default, so as not to break the current implementation.

  • ServerVariables render correctly within Scalar:

Screenshot_2026-02-16_at_13.49.42

Screenshot_2026-02-16_at_13.49.35

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Related to #586604 (closed)

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