[AE-96] Fix API docs

[cbguder]

References

JIRA: AE-96

Description

On case-sensitive filesystems, mdbook clean generates docs/api.md (apparently due to the references in SUMMARY.md and intro.md), causing an empty API docs page to be generated.

Ensuring the case matches between the references and the file on disk seems to fix the issue.

PR Review Checklist

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• [x] This PR conforms to the Contribution Guidelines
• [x] This PR conforms to the Opsec policies
• [ ] Functional and performance test coverage has been expanded and maintained (if applicable)
• [ ] The [load test: (abort|warn)] keywords are applied (if applicable)
• [x] Documentation has been updated
• [x] The PR title starts with the JIRA issue reference, format [DISCO-####], and has the same title