[sda-download] test for visa issuer

[kostas-kou]

As a sda-developer
I want to have a test about the the visa issuer in iss.json file
so that data are delivered only in case that visa issuer is in that json file

Additional context
This issue created from the following checkpoint:
Only if the visa issuer is in the iss.json file data should be delivered to the end user.
in this issue