Add digital signature to SharpYaml.dll

[ShaunLoganOracle]

Please add a digital signature to SharpYaml.dll

Digital signatures protect files from tampering, and enable users to verify the signer based on a signing certificate.

Reference: https://docs.microsoft.com/en-us/dotnet/framework/tools/signtool-exe

Update: our team uses SharpYaml.dll via MSFT's OpenApi.NET (which is signed). We don't build from source, rather we use the NuGet package mgr from Visual Studio to get SharpYaml.dll.