add soda_synthetic_dialogue dataset

[jquesnelle]

resolves #415

This creates the "🥤SODA Synthetic Dialogue" dataset following the instructions as described in datasets.md. Since this is the first dataset added to the repo, I followed the instructions closely including using all the provided templates so as to have a good first example for other datasets. To this end I re-created the dialogue generation in a prepare.py rather than pulling the data directly from the Colab notebook.

[huu4ontocord]

This looks good to me. Thank you @jquesnelle

[github-actions[bot]]

:x: pre-commit failed. Please run pre-commit run --all-files locally and commit the changes. Find more information in the repository's CONTRIBUTING.md