docs(CertificateManager/ICertificateManager): clarify API

[joshtrichards]

• Resolves: #

Summary

This updates both CertificateManager and ICertificateManager to keep the concrete implementation and public contract aligned - and to fully document the OCP API.

Notes

Only functional change is making the CertificateManager::createCertificateBundle() helper private. It was already not part of the interface and is only used internally within the implementation itself.

TODO

• Possibly make one more pass back through the implementation to drop some bits now better covered in the interface docs

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI