need a way to shut down rooms

Use case: we're running a conference (say, IEEE VR), and for whatever reason we want to shut down a bunch of the rooms:

* bad behavior that we want to immediately terminate
* the server isn't dealing with the load and we want to shut off some rooms to reduce the load until we have a break and can up the server count via Cloud Formation

I'm honestly more concerned with the later. If we discover we've underestimated and some session draws more people than expected (e.g., all rooms, all lobbies are full), we may want to nuke some temporarily so the talk can continue, without having to bring the whole thing down

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/HUBS-1025)

The issue names no files, tests, or entry points; start by reviewing the linked Jira task HUBS-1025 and the room and server-management context. Done should provide a way to temporarily shut down selected rooms to reduce load or stop bad behavior without taking down the whole instance.

Written by the indexing model from the issue text.