add group and endgroup commands

src/Runner.Common/ExtensionManager.cs

@@ -56,6 +56,8 @@ private List<IExtension> LoadExtensions<T>() where T : class, IExtension
                     Add<T>(extensions, "GitHub.Runner.Worker.WarningCommandExtension, Runner.Worker");
                     Add<T>(extensions, "GitHub.Runner.Worker.ErrorCommandExtension, Runner.Worker");
                     Add<T>(extensions, "GitHub.Runner.Worker.DebugCommandExtension, Runner.Worker");
+                    Add<T>(extensions, "GitHub.Runner.Worker.GroupCommandExtension, Runner.Worker");
+                    Add<T>(extensions, "GitHub.Runner.Worker.EndGroupCommandExtension, Runner.Worker");
                     break;
                 default:
                     // This should never happen.

src/Runner.Worker/ActionCommandManager.cs

@@ -506,5 +506,29 @@ private static class IssueCommandProperties
             public const String Line = "line";
             public const String Column = "col";
         }
+
+    }
+
+    public sealed class GroupCommandExtension : GroupingCommandExtension
+    {
+        public override string Command => "group";
+    }
+
+    public sealed class EndGroupCommandExtension : GroupingCommandExtension
+    {
+        public override string Command => "endgroup";
+    }
+
+    public abstract class GroupingCommandExtension : RunnerService, IActionCommandExtension
+    {
+        public abstract string Command { get; }
+        public Type ExtensionType => typeof(IActionCommandExtension);
+
+        public void ProcessCommand(IExecutionContext context, string line, ActionCommand command, out bool omitEcho)
+        {
+            var data = this is GroupCommandExtension ? command.Data : string.Empty;
+            context.Output($"##[{Command}]${data}");
+            omitEcho = true;
+        }
     }
 }