Support nested tasks

[kris524]

There is a bug: when you have a parent-child relationship in Notion, currently we just add the tasks on the same level in Google Tasks. However, GT, supports up to one level of depth between tasks. If you were to have a parent-child in Notion tasks, and in google it will end up both on the top level, If you were to delete the parent in GT, this will delete both tasks in Notion (the parent and child), not just the parent, and when the update is ran again, the following error is raised:

notion_client.errors.APIResponseError: Can't update a block with an archived ancestor. You must unarchive the ancestor before updating.