Initial support for converting the mappings to a Pact(flow) json file (#748)

* WithDescription

* WithConsumer / WithProvider

* x

* .

* .

* .

* .

* fix

* pact

* nullable

* ficx

* .

* fix

src/WireMock.Net/Serialization/JsonSerializationConstants.cs

@@ -20,5 +20,11 @@ namespace WireMock.Serialization
         {
             DateParseHandling = DateParseHandling.None
         };
+
+        public static readonly JsonSerializerSettings JsonSerializerSettingsPact = new JsonSerializerSettings
+        {
+            Formatting = Formatting.Indented,
+            NullValueHandling = NullValueHandling.Ignore
+        };
     }
 }