Add MappingBuilder to build mappings in code and export to Models or JSON (#869)

* MappingBuilder

* .

* ...

* sc

* t

* .

src/WireMock.Net/IMappingBuilder.cs

@@ -0,0 +1,43 @@
+using WireMock.Admin.Mappings;
+using WireMock.Matchers.Request;
+using WireMock.Server;
+
+namespace WireMock;
+
+/// <summary>
+/// IMappingBuilder
+/// </summary>
+public interface IMappingBuilder
+{
+    /// <summary>
+    /// The given.
+    /// </summary>
+    /// <param name="requestMatcher">The request matcher.</param>
+    /// <param name="saveToFile">Optional boolean to indicate if this mapping should be saved as static mapping file.</param>
+    /// <returns>The <see cref="IRespondWithAProvider"/>.</returns>
+    IRespondWithAProvider Given(IRequestMatcher requestMatcher, bool saveToFile = false);
+
+    /// <summary>
+    /// Gets all the mappings as a list.
+    /// </summary>
+    /// <returns>A list from <see cref="MappingModel"/>s.</returns>
+    MappingModel[] GetMappings();
+
+    /// <summary>
+    /// Convert all mappings to JSON.
+    /// </summary>
+    /// <returns>JSON</returns>
+    string ToJson();
+
+    /// <summary>
+    /// Save all mappings as a single JSON to a file.
+    /// </summary>
+    /// <param name="path">The file to write to.</param>
+    void SaveMappingsToFile(string path);
+
+    /// <summary>
+    /// Save all mappings as multiple JSON files (each file is 1 mapping).
+    /// </summary>
+    /// <param name="folder">The folder to write the files to.</param>
+    void SaveMappingsToFolder(string folder);
+}