Document OpenAPI 3.2 support

[brandonmcconnell]

Documentation changes

Adds an OpenAPI 3.2 features section to api-playground/openapi-setup.mdx and updates the supported-version statements to include 3.2. Covers tag hierarchies, query and additionalOperations (including the frontmatter form for custom methods), in: querystring, itemSchema streaming, dataValue / serializedValue, device authorization and other security scheme additions, defaultMapping, serialization rules (style: cookie, allowReserved, positional encodings), document-level fields ($self, servers[].name, response summary, components.mediaTypes), and the documented limitations from the coverage matrix in mint#11562.

Hold until the openapi-3.2 Unleash flag is enabled in production. The feature ships gated behind that flag across the mint stack and server#8382; merging this before the flag is on would document behavior customers cannot yet use.

Closes ENG-11064 (docs portion)

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For Reviewers

When reviewing documentation PRs, please consider:

✅ Technical accuracy

• Code examples work as written (each YAML/MDX snippet mirrors a fixture in the mint stack's tests)
• Commands and configurations are correct
• Links resolve to the right destinations
• Prerequisites and requirements are accurate

✅ Clarity and completeness

• Instructions are clear and easy to follow
• Steps are in logical order
• Nothing important is missing
• Examples help illustrate the concepts

✅ User experience

• A new user could follow these docs successfully
• Common gotchas or edge cases are addressed (Limitations subsection)
• Error messages or troubleshooting guidance is helpful

  

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