tools,doc: fix json result of grouped optional params

Pull Request check-list

• Does make -j8 test (UNIX) or vcbuild test nosign (Windows) pass with this change (including linting)?
• Is the commit message formatted according to CONTRIBUTING.md?
• If this change fixes a bug (or a performance problem), is a regression test (or a benchmark) included?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

Affected core subsystem(s)

• tools, doc

Description of change

fixes #5976 (closed)