ChatGPT constructor: add slow-down option so that it can also be used if you don't have a paid ChatGPT account

[wvdvegte]

Prototypes version

0.21.1

Orange version

3.36.2

Expected behavior and actual behavior

I wanted to try the cookie-mining example, but, as a non-paying ChatGPT 3.5 user, I'm not allowed to send more than 3 requests per minute. It would be nice to be able to try this out, even if it means that the workflow has to run overnight. So perhaps add a checkbox "reduce requests per minute (for non-paying users, slow!)" ...