TaskTree: Remove GroupConfig / GroupAction

Use TaskAction for dynamic group setup. Get rid of possibility
of selecting group's children to be started inside group setup.
Use dynamic children's setup instead, so that each individual child
may decide itself whether it wants to be started or not.

Change-Id: Ie31f707791db0dc26be92663ca6238b8e49c3b98
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/git/gitclient.cpp

@@ -344,8 +344,8 @@ ShowController::ShowController(IDocument *document, const QString &id)
 
     const auto desciptionDetailsSetup = [storage] {
         if (!storage->m_postProcessDescription)
-            return GroupConfig{GroupAction::StopWithDone};
-        return GroupConfig();
+            return TaskAction::StopWithDone;
+        return TaskAction::Continue;
     };
 
     const auto setupBranches = [this, storage](QtcProcess &process) {