fix: update the section heading case to conform to our standard

[ryanpq]

Updates section heading cases in documentation to follow most recent PRs

Description

References

Review Checklist

• [x] I have clicked on "allow edits by maintainers".
• [ ] I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• [ ] The correct base branch is being used, if not main
• [ ] I have added tests to validate that the change in functionality is working as expected

[github-actions[bot]]

PR Preview Action v1.4.7 :---: :rocket: Deployed preview to https://openfga.github.io/openfga.dev/pr-preview/pr-847/ on branch gh-pages at 2024-09-23 10:18 UTC