Support runner upgrade messages (#2231)

Co-authored-by: Thomas Boop <52323235+thboop@users.noreply.github.com>

src/Sdk/DTWebApi/WebApi/RunnerRefreshMessage.cs

@@ -0,0 +1,49 @@
+using Newtonsoft.Json;
+using System;
+using System.Runtime.Serialization;
+
+
+namespace GitHub.DistributedTask.WebApi
+{
+    [DataContract]
+    public sealed class RunnerRefreshMessage
+    {
+        public static readonly String MessageType = "RunnerRefresh";
+
+        [JsonConstructor]
+        internal RunnerRefreshMessage()
+        {
+        }
+
+        public RunnerRefreshMessage(
+            Int32 runnerId,
+            String targetVersion,
+            int? timeoutInSeconds = null)
+        {
+            this.RunnerId = runnerId;
+            this.TimeoutInSeconds = timeoutInSeconds ?? TimeSpan.FromMinutes(60).Seconds;
+            this.TargetVersion = targetVersion;
+        }
+
+        [DataMember]
+        public Int32 RunnerId
+        {
+            get;
+            private set;
+        }
+
+        [DataMember]
+        public int TimeoutInSeconds
+        {
+            get;
+            private set;
+        }
+
+        [DataMember]
+        public String TargetVersion
+        {
+            get;
+            private set;
+        }
+    }
+}