Add server certificate to AddIceRpcServer docfx examples

[bernardnormier]

The docfx examples for ServerServiceCollectionExtensions / AddIceRpcServer don't show the installation of the server certificate.

See GenericHost example for the proper setup:

        // Load and register the server certificate as a singleton so it stays alive and gets disposed.
        services.AddSingleton<X509Certificate2>(sp =>
            X509CertificateLoader.LoadPkcs12FromFile(
                Path.Combine(
                    hostContext.HostingEnvironment.ContentRootPath,
                    hostContext.Configuration.GetValue<string>("Certificate:File")!),
                password: null,
                keyStorageFlags: X509KeyStorageFlags.Exportable));

        // Bind the server options to the "appsettings.json" configuration "Server" section, and add a Configure
        // callback to configure its authentication options.
        services
            .AddOptions<ServerOptions>()
            .Bind(hostContext.Configuration.GetSection("Server"))
            .Configure<X509Certificate2>((options, serverCertificate) =>
                options.ServerAuthenticationOptions = CreateServerAuthenticationOptions(serverCertificate));

As a result, these docfx examples are incomplete and potentially confusing.

For the GenericHost example, we use a helper to create the server authentication options, but not the the docfx examples. Maybe we should add this helper to the docfx examples?