Make cloud functions datasets processing use elpis core library

[harrykeightley]

@nicklambourne please don't muder me- this looks intimidating but is really just massive deletion of functions which now live in the elpis core library. The additions are from the poetry lock file.

Changes:

1. Add elpis as a poetry dependency, and fix torch version to avoid some dependency errors.
2. Delete all code now covered by elpis core library for dataset processing.
3. Extend the elpis core Dataset and ProcessingBatch classes to include cloud specific attributes (e.g. user_id). These become CloudDataset and ProcessingJob respectively.