Slash commands

[dougarley]

https://gist.github.com/advaith1/287e69c3347ef5165c0dbde00aa305d2

[fusion2004]

I was waiting for commando to support them, but of course I just found out the discord.js team is abandoning commando in favor of sapphire, which also doesn't support them yet (there is a draft PR open to support them).

At this point, I think the better path may be to implement the commando features we're using ourselves and implement commands with https://github.com/Snazzah/slash-create
https://slash-create.js.org/#/docs/main/latest/examples/command