Store model in transcription metadata

[stakats]

Maybe I am missing something, but are we not storing the model used in Transkribus? We could add something like this for example, after transcription.config.jobId = job.id:

transcription.config.model = config.model
transcription.config.htr = htr

[stakats]

(might also want to make it clear that it's Transkribus too, as well as any important versioning data there.)