Create a tidied participant data.table
tidy_participants(stage_profiles, stage_uuids)
| stage_profiles | the output of `query_stage_profiles()`.  | 
    
|---|---|
| stage_uuids | the output of `query_stage_uuids()`.  | 
    
a data.table
the `update_ts` field can be used to infer the signup datetime of each user.