Upgrade to API v8

[SquidDev]

v6/v7 are being deprecated in two months (1 May), so the bot will break. We've got a couple of options here:

• Update Discord.py 2.0. The original developer is back and its being maintained again (though still no stable release).
• One of the alternative discord.py forks out there.
• Rewrite in something fun (F# probably, using Discord.NET).

A little worried that discord.py is going to stop being maintained again. Though maybe we just update for now and think about porting another day - will have to see how much work updating (and switching from interactions.py - wow this has come a long way since it was discord-py-slash-command).