Add room ban support to virtualUsers

Follow-up to https://gitlab.com/gitlab-org/gitter/webapp/-/issues/1076

Add room ban support to virtualUsers

• API for adding and removing bans
• When a new message/edit comes through, apply bans

Relevant code

• server/api/v1/rooms/bans.js
• modules/permissions/lib/policies/create-base-policy.js#L214-217
• scripts/utils/ban-user-from-room.js