Support for internal signaling federation

[danxuliu]

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From #12604

Joining/leaving with the federated session IDs seems to work with internal signaling too (and the participant status is eventually updated in the sidebar), but is something else needed? For example, relaying the ping from the federated server to the host or something like that.

It should be verified if cleaning participants works as intended (it seems that only secondary sessions are cleaned when inactive, but if a single session is kept in the room without a ping it is not cleaned), as it could be relevant for internal signaling if the behaviour is changed

• Related: fix(federation): Ignore outdated sessions when checking for active se… #12741