[AOAI] Update optional details property

[minhanh-phan]

Update the TypeSpec for 2024-08-01-preview and 2024-09-01-preview to mark the property as optional for missing files from #30632 and #30887

[openapi-pipeline-app]

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[openapi-pipeline-app]

Generated ApiView

Language	Package Name	ApiView Link
Swagger	AzureOpenAI	https://apiview.dev/Assemblies/Review/6693675ace534d4aa3159f202a195962?revisionId=75244a12fc0c4673aeb0c4c04c58e6b4