Matrix moderation

For this year's Canvas, the main server will directly instruct Synapse to do moderation actions. In future events this should be centralized in a separate service, to also allow other event servers to manage Matrix moderation actions.

Matrix moderation tasks shouldn't be directly tied to actions done on Canvas, but moderators should easily have the ability to ban people.

Banning on the Matrix side should not equivalate to deactivation, but locking the account instead, a non-permanent action. If fediverse Matrix accounts become a permanent thing on aftermath.gg, this would instead be banning from the Canvas Matrix space (if they did not violate aftermath.gg terms).

When a user gets banned on the Canvas side, the moderator should have the option to ban them from the #canvas-general channel on Matrix to prevent issues.