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.Abstractions/Admin/Mappings/MappingModel.cs

@@ -24,6 +24,11 @@ namespace WireMock.Admin.Mappings
         /// </summary>
         public string Title { get; set; }
 
+        /// <summary>
+        /// The description.
+        /// </summary>
+        public string Description { get; set; }
+
         /// <summary>
         /// The priority. (A low value means higher priority.)
         /// </summary>