Reset ready status after timer

[SelinaBuff]

Discussed in #3271

^{Originally posted by SelinaBuff August 9, 2023}
We noticed during the last retrospective that the Ready status of the participants is not automatically reset, even though the timer has expired and the voting sessions have started. In the best case, everyone is automatically marked as "undone" again before the next action like "Voting" is triggered.
Or the moderator confirms via a popup that the "ready status" of the participants is reset before the voting session is started.