Fix ClientCertificates in csharp configuration for client generation.

Created by: paritoshgote-msft

Fixes the injection of ClientCertificates in Configuration.mustache for csharp netcore and netcore-functions.

ClientCertificates was not being configured properly as part of the csharp client generation. These changes have been tested locally. Original issue link: https://github.com/OpenAPITools/openapi-generator/issues/6940

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