Resolve "Conference UI: Implement Live Subtitles"

There is still a bug when activating the transcription service. If you change the language on an active transcription service currently no request will be sent, so the language will not change, because we only check if the switch state (service on/off) has changed. If we send a request to activate, while the service is active, we get an error, that's what I'm trying to avoid by checking if something has changed. We can alternatively just handle the error differently.

Closes #3353 (closed)