Define ways of being notified if a room is created or entered in the cloud

Either for personal or enterprise use, it may be desirable to get notified when a room is entered or created, without coupling the room to something like Discord.

For example, if I keep a personal hubs cloud running, I am currently imaging having scenes as room templates, that anyone can visit and create rooms, to experience the "spaces" of my personal VR home. I would like to be notified whenever this happens, so I can consider dropping in and chatting with whomever is visiting my "home". Or, at least be able to monitor use.

Perhaps a way to do this would be to have a version of the discord bot that links to the entire cloud, but does NOT require someone to be authenticated / signed into the discord to use it. This would require a different association between discord channels and rooms (since rooms might be created on the fly)

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/HUBS-1017)

No files, tests, or entry points are identified in the issue. Begin by defining the notification requirements for room creation and entry, including personal and enterprise use and the proposed Discord integration; done means an agreed implementation scope and notification design.

Written by the indexing model from the issue text.