Fix a typo in openai.adoc

[Hyune-c]

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• @RequestParam annotation was incorrectly written as P@RequestParam
• fix generateStream example
• Improved API visibility

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• Sign the contributor license agreement ✅
• Rebase your changes on the latest main branch and squash your commits ✅
• Add/Update unit tests as needed ✅
• Run a build and make sure all tests pass prior to submission ✅