Doxygen: use MARKDOWN_ID_STYLE = GITHUB

[scpeters]

🦟 Bug fix

Fixes errors in gazebosim/gz-sensors#516

Summary

This allows linking to subsections of a tutorial and fixes the following error from
gazebosim/gz-sensors#516:

tutorials/install.md:138: warning: unable to resolve reference to 'install-prerequisites' for \ref command

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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