Support for Forum Channels

[Lepras]

I don't see any mention of forum channels on the issues or the roadmap so here it goes.

Discordgo seems to have the support seeing this PR and their docs.

You can learn more about discord forums here.

We can use matrix threads for bridging this type of content and messages.

[Lepras]

Oh lol wrong repo, I shouldn't make issues on mobile.

Sorry for this, gonna close this and make the issue in the right repo.