Feature request: Retrieve 'shuffle$group' through api

[xpressio]

Dear developers,

I would like to suggest a new feature for the API: the possibility to retrieve 'shuffle$group' information. While getting this information can be achieved through "formr_shuffled()" from the formr R package, an API solution could have additional benefits, such as token authentication or the use in contexts, where the R package is not available.

Thanks for considering this and big thank you for developing formr - we are about to finish our first pilot study with it and are really pleased with the overall experience of conducting a study in formr!

Best
Max