fix: Rate limit error when executing requests too quickly

[rswilem]

I have created this very simple fix for the following error:

django.core.exceptions.ImproperlyConfigured:

{"success": false, "error": {"code": 106, "type": "rate_limit_reached", "info": "You have exceeded the maximum rate limitation allowed on your subscription plan. Please refer to the \"Rate Limits\" section of the API Documentation for details. "}}

It seems the Vatlayer API prevents two fast consecutive requests. Therefore I've added a small delay between the requests.

For reference, the error that pops up in Saleor:

[nvrebcevic]

I welcome this change very well. It should be merged as soon as possible since manage.py get_vat_rates is practically useless without this sleep, at least for the free subscription Vatlayer account.

[yevheniidehtiar]

guys, still actual