OpenApiResponseBody is obsolete but mentioned in docs

https://github.com/Azure/azure-functions-openapi-extension/blob/main/docs/openapi-core.md#expose-endpoints-to-openapi-document

This page uses `OpenApiResponseBody` instead of `OpenApiResponseWithBody`, but the former is [marked obsolete](https://github.com/Azure/azure-functions-openapi-extension/blob/main/src/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core/Attributes/OpenApiResponseBodyAttribute.cs#L9)

Open docs/openapi-core.md at the “Expose endpoints to OpenAPI document” section and compare its attribute name with the linked obsolete OpenApiResponseBodyAttribute declaration. Update the documentation to use OpenApiResponseWithBody, then verify that the referenced example no longer mentions the obsolete attribute.

Written by the indexing model from the issue text.