Add TimeSettings (Start, End and TTL) (#661)

* time

* .

* UT

* using JetBrains.Annotations;

src/WireMock.Net.Abstractions/Admin/Mappings/MappingModel.cs

@@ -1,4 +1,5 @@
-using System;
+using System;
+using WireMock.Models;
 
 namespace WireMock.Admin.Mappings
 {
@@ -13,6 +14,11 @@ namespace WireMock.Admin.Mappings
         /// </summary>
         public Guid? Guid { get; set; }
 
+        /// <summary>
+        /// Gets or sets the TimeSettings when which this mapping should be used.
+        /// </summary>
+        public TimeSettingsModel TimeSettings { get; set; }
+
         /// <summary>
         /// The unique title.
         /// </summary>