Support specifying a full certificate chain in HttpsConnectionAdapterOptions

[davidfowl]

public class HttpsConnectionAdapterOptions
{
    public X509Certificate2 ServerCertificate { get; set; }
+   public X509Certificate2Collection ServerCertificateChain { get; set; }
}

Configuration:

For configuration, we'll support the full cert chain in Path:

// "CertificateName": {
     //     "Path": "testCert.pem/pfx",
     //     "KeyPath": "key.pem",

This depends on dotnet/runtime#35844

[Pilchie]

Moving this to RC2, since the PR isn't ready yet, and we're out of time for RC1