Adding "Discussion" and "Comment" capabilities

First of all, I wanted to say **thank you** for this implementation of the Notion API 🙌
It is really really useful, it is crazy all the automation opportunities it brings and shows the real potential of Notion.

I was wondering if you had explored the possibility to handle _Discussion_ and _Comment_? Allowing to open a new _Discussion_ on a block, to add a _Comment_ to a _Discussion_ – and even to listen to new _Comments_ – like you manage to do it with live-update of _Blocks_?

Once again, thank you for this repo – it is already really amazing 👍

Start by reviewing the existing block live-update handling, then determine how this client represents discussions and comments. The work is complete when it can open a discussion on a block, add comments to a discussion, and listen for new comments, with the required API behavior confirmed.

Written by the indexing model from the issue text.