Endpoint to delete an existing task by its ID. Only the original creator of the task is authorized to delete the task.
Args: task_id (str): The unique identifier of the task to be deleted.
Returns: dict: A confirmation message on successful deletion.
Raises: HTTPException 403: If the current user is not authorized to delete the task. HTTPException 404: If the task is not found. HTTPException 500: If a runtime error occurs during deletion.