Add order by for assignee no sort issue (#20053)

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/user/user.go

@@ -1314,3 +1314,10 @@ func IsUserVisibleToViewer(ctx context.Context, u, viewer *User) bool {
 	}
 	return false
 }
+
+func GetOrderByName() string {
+	if setting.UI.DefaultShowFullName {
+		return "full_name, name"
+	}
+	return "name"
+}