Youtube livestream support

[fractal161]

A large portion of the classic tetris audience now watches content through youtube livestreams, so it would be great if they could also use the bot.

[fractal161]

Some notes on what this would entail:

• Youtube allows multiple live broadcasts per channel, so each is given its own id and its own chat. It's possible that we can use push notifications to avoid having to poll every single channel for updates on this, but I'm not 100% clear yet on if live broadcasts/premieres or anything with a chat count as "uploading a video".
• The only method for reading chat seems to be polling-based based on how the api looks. I'm not sure of the best way to handle this, but I think async should suffice?
• We should probably look into the developer policies to make sure we can request api quota extensions if that ever becomes an issue. Overall, this seems surprisingly doable? I'm worried that having ephemeral chats may present issues that the bot hasn't needed to deal with so far, but I suppose we worry about that when we get there.

Reading for later:

• Get chat messages: https://developers.google.com/youtube/v3/live/docs/liveChatMessages/list
• Send chat messages: https://developers.google.com/youtube/v3/live/docs/liveChatMessages/insert
• Examples: https://gist.github.com/w3cj/4f1fa02b26303ae1e0b1660f2349e705

[michaelelin]

API seems pretty simple.

The only method for reading chat seems to be polling-based based on how the api looks. I'm not sure of the best way to handle this, but I think async should suffice?

Yeah, running an async thread for each stream seems reasonable. It seems like we just need some mechanism for starting/stopping those threads based on which of those streams are live (and then maybe some model for YouTube channels so we can store which ones the bot should listen to).

What's the process for adding a new YouTube channel to the bot?