fix: avoid double fixture load for clientvarcondition

[npazosmendez]

I noticed running python manage.py afipmetadata multiple times loaded the ClientVatCondition fixture multiple times. This fixes that using natural keys, just like GenericAfipType does.

Piggybacking two minor changes:

• Add Spanish translations for ClientVatCondition strings
• Remove the (code) string from ClientVatCondition's __str__, matching what GenericAfipType does

[WhyNotHugo]

CI failed due to running too frequently (El CEE ya posee un TA valido para el acceso al WSN solicitado !).

[WhyNotHugo]

All tests pass locally.

Applied, thanks.