Add option to ProxySettings to append guid to mapping file (#838)

* Add option to ProxySettings to append guid to mapping file

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src/WireMock.Net/Settings/ProxyAndRecordSettings.cs

@@ -58,4 +58,9 @@ public class ProxyAndRecordSettings : HttpClientSettings
     /// Default value is false.
     /// </summary>
     public bool UseDefinedRequestMatchers { get; set; }
+
+    /// <summary>
+    /// Append an unique GUID to the filename from the saved mapping file.
+    /// </summary>
+    public bool AppendGuidToSavedMappingFile { get; set; }
 }