Support public conversations and guests in breakout rooms

[nickvergessen]

Currently guests identity depends on the session, so we can not move them to another room like required by breakout rooms. When they join the room as a guest, they would generate a new identify which also means they lost track of their old on.

Related technical issues:

• Guests can immediately re-join a public meeting after being removed by the moderator #1423
• No messages sent to guests by the external signaling server when rooms are updated #2146
• Add feature to be able to disable access link to external users without removing all guest users from the conference #7302