Document OpenAPI 3.2 support - #7436

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 mint stack has merged and the server has picked up the published packages. There is no feature flag: 3.2 documents are accepted by their declared version once the mint stack (#11550 → #11562) and server#8382 are deployed; merging this earlier would document behavior customers cannot yet use. Features that merge later in the stack can be documented incrementally if the stack lands in pieces.

Closes ENG-11064 (docs portion)

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