* ref(transcriptions): refactor transcriptions api

* ref(transcriptions): refactor usage of translation label

Extend IFrame API to allow adding a transcriber in the room without the subtitles needing to be visible.
Allow transcription chunk messages to be passed through the IFrame API if a transcriber is present.
Clean-up transcription messages sent through the IFrame API to not include timeout field and possible conflicting states (stable / unstable /final)

* fix linting

* code review: extend api message to match webhook format