Consider replacing user credentials with tokens or keys in a deployment procedure

[marekhorst]

This is a direct follow up of #1292 and #1293 tasks. According to the documentation available in our gitlab repository (hosting the deployment configuration):

https://git.icm.edu.pl/openaire/iis-deployment/-/wikis/Deployment-by-Jenkins https://git.icm.edu.pl/openaire/iis-deployment/-/wikis/Integration-tests-by-Jenkins

there are specific user credentials used (login+key pair) but apparently gitlab allows relying on deploy tokens or deploy keys for such deployment related use cases: https://git.icm.edu.pl/help/user/project/deploy_tokens/index.md#deploy-tokens https://git.icm.edu.pl/help/user/project/deploy_keys/index

Therefore we should check whether we could rely on that instead of involving any particular user credentials.