Implement Enterprise Search Indexing Client and unit/integration tests

Octokit/Models/Request/Enterprise/SearchIndexingTarget.cs

@@ -0,0 +1,12 @@
+namespace Octokit
+{
+    public class SearchIndexTarget
+    {
+        public SearchIndexTarget(string target)
+        {
+            Target = target;
+        }
+
+        public string Target { get; protected set; }
+    }
+}