Description of problem:
When RHSM is used during the IPU, the proxy defined in RHSM is used, as it generates the redhat.repo file with the proxy setting.
But in case of RHUI repositories, there is no equivalent. Usually customers choose /etc/yum.conf to define it, but this is not taken into account in the target userspace container (/etc/yum/* are symlinked to /etc/dnf/* but not the main config file).

Version-Release number of selected component (if applicable):
leapp-upgrade-el7toel8-0.15.0-6.el7_9

How reproducible:
Always for AWS

Steps to Reproduce:
1. Try to upgrade a RHEL 7.9 OS (PAYG on AWS, not BYOS) behind a proxy.

Actual results:
Unable to reach RHUI repos.

Additional info:

• to workaround the issue, the proxy has been added to /etc/dnf/dnf.conf, and then the DNF config has been added by patching /usr/share/leapp-repository/repositories/system_upgrade/common/actors/scanfilesfortargetuserspace/libraries/scanfilesfortargetuserspace.py.

• the suggested feature I mentioned in rhbz#2040706 could help