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/IRequestMessage.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using WireMock.Types;
 using WireMock.Util;
@@ -28,7 +28,7 @@ namespace WireMock
         /// <summary>
         /// The ProxyUrl (if a proxy is used).
         /// </summary>
-        string ProxyUrl { get; }
+        string ProxyUrl { get; set; }
 
         /// <summary>
         /// Gets the DateTime.
@@ -83,7 +83,7 @@ namespace WireMock
         /// <summary>
         /// The body.
         /// </summary>
-        IBodyData BodyData { get; }
+        IBodyData? BodyData { get; }
 
         /// <summary>
         /// The original body as string. Convenience getter for Handlebars.