Use Arcade signing validation in pipeline

Currently the pipeline does not use [`post-build.yml`](https://github.com/dotnet/NuGet.BuildTasks/blob/main/eng/common/templates-official/post-build/post-build.yml) template, but using this template will allow for Arcade to perform different validations such as NuGet and Code Sign validation. Allowing for `post-build.yml`, will need some reconfiguration of this Arcade pipeline though.