Grpc: Fix parsing null value for google.protobuf.Timestamp (#1293)

* Add another example for Grpc client + mapping

* <PackageReference Include="ProtoBufJsonConverter" Version="0.9.0" />

examples/WireMock.Net.Console.GrpcClient/WireMock.Net.Console.GrpcClient.csproj

@@ -5,6 +5,7 @@
         <TargetFramework>net8.0</TargetFramework>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
+        <LangVersion>latest</LangVersion>
     </PropertyGroup>
 
     <ItemGroup>
@@ -18,6 +19,7 @@
 
     <ItemGroup>
         <Protobuf Include="greet.proto" GrpcServices="Client" />
+        <Protobuf Include="policy.proto" GrpcServices="Client" />
     </ItemGroup>
 
-</Project>
+</Project>