feat(task-management): enhance task management UI with subtask functionality

- Updated task list components to support subtasks, including TaskRowWithSubtasks for rendering tasks with their subtasks.
- Introduced AddSubtaskRow for adding new subtasks directly within the task list.
- Enhanced TaskRow to handle task expansion and display subtask counts.
- Implemented optimistic updates for subtask creation to improve user experience.
- Added loading states for subtasks to provide visual feedback during data fetching.
- Refactored task management slice to manage subtasks and their loading states effectively.

worklenz-frontend/public/locales/en/task-drawer/task-drawer-info-tab.json

@@ -24,7 +24,7 @@
   },
   "subTasks": {
     "title": "Sub Tasks",
-    "add-sub-task": "+ Add Sub Task",
+    "add-sub-task": "Add Sub Task",
     "refresh-sub-tasks": "Refresh Sub Tasks"
   }
 }

worklenz-frontend/public/locales/en/task-drawer/task-drawer.json

@@ -43,7 +43,7 @@
     },
     "subTasks": {
       "title": "Sub Tasks",
-      "addSubTask": "+ Add Sub Task",
+      "addSubTask": "Add Sub Task",
       "addSubTaskInputPlaceholder": "Type your task and hit enter",
       "refreshSubTasks": "Refresh Sub Tasks",
       "edit": "Edit",