Give every user different data

data-env.vl.js reads one row of data/widgets.csv for each iteration, so users do not all send the same request.

API_KEY=demo-key vegaload run -vus 5 -duration 10s -data data/widgets.csv -secret-env API_KEY data-env.vl.js

The sample app fails about 3 percent of creates on purpose, so a few checks fail. That is expected. In the script, data.widgets.next() is the next row, and data.widgets.random() is any row.