Expose transcription in List elements endpoints

Refs https://redmine.teklia.com/issues/7907

The list elements endpoint already serve optionally classifications. We should do the same for transcriptions, as it would allow for faster retrieval of transcriptions in API scripts. This would be unused by the frontend.

The feature should be triggered by a with_transcriptions=true|false query parameter, defaulting to false. The transcription serializer should include:

• id
• text
• confidence
• orientation
• worker run object (id + summary)