Make JobTelemetryType a string

src/Sdk/DTWebApi/WebApi/JobTelemetry.cs

@@ -12,6 +12,6 @@ public class JobTelemetry
         public string Message { get; set; }
 
         [DataMember(EmitDefaultValue = false)]
-        public string Type { get; set; }
+        public JobTelemetryType Type { get; set; }
     }
 }

src/Sdk/DTWebApi/WebApi/JobTelemetryType.cs

@@ -0,0 +1,13 @@
+using System.Runtime.Serialization;
+
+namespace GitHub.DistributedTask.WebApi
+{
+    public enum JobTelemetryType
+    {
+        [EnumMember]
+        General = 0,
+
+        [EnumMember]
+        ActionCommand = 1,
+    }
+}