Leapp preupgrade fails on Satellite server behind web proxy

Issue

• Running the leapp preupgrade command on a Satellite server yields the following error:

[ERROR] Actor: target_userspace_creator
Message: Unable to install RHEL 8 userspace packages.
Summary:
    Details: Command ['systemd-nspawn', '--register=no', '--quiet', '-D', '/var/lib/leapp/scratch/mounts/root_/system_overlay', '--setenv=LEAPP_UPGRADE_PATH_TARGET_RELEASE=8.6', '--setenv=LEAPP_NO_RHSM=0', '--setenv=LEAPP_EXPERIMENTAL=0', '--setenv=LEAPP_UPGRADE_PATH_FLAVOUR=default', '--setenv=LEAPP_COMMON_TOOLS=:/etc/leapp/repos.d/system_upgrade/el7toel8/tools', '--setenv=LEAPP_COMMON_FILES=:/etc/leapp/repos.d/system_upgrade/common/files:/etc/leapp/repos.d/system_upgrade/el7toel8/files', '--setenv=LEAPP_IPU_IN_PROGRESS=7to8', '--setenv=LEAPP_UNSUPPORTED=0', '--setenv=LEAPP_EXECUTION_ID=9ec32874-4554-4975-a678-c4d201644e95', '--setenv=LEAPP_HOSTNAME=$EXAMPLE_HOSTNAME', 'dnf', 'install', '-y', '--nogpgcheck', '--setopt=module_platform_id=platform:el8', '--setopt=keepcache=1', '--releasever', u'8.6', '--installroot', '/el8target', '--disablerepo', '*', '--enablerepo', u'rhel-8-for-x86_64-baseos-rpms', '--enablerepo', u'satellite-maintenance-6.11-for-rhel-8-x86_64-rpms', '--enablerepo', u'satellite-6.11-for-rhel-8-x86_64-rpms', '--enablerepo', u'rhel-8-for-x86_64-highavailability-rpms', '--enablerepo', u'rhel-8-for-x86_64-appstream-rpms', 'dnf', 'dnf-command(config-manager)'] failed with exit code 1.
    Stderr: Failed to create directory /var/lib/leapp/scratch/mounts/root_/system_overlay//sys/fs/selinux: Read-only file system
            Failed to create directory /var/lib/leapp/scratch/mounts/root_/system_overlay//sys/fs/selinux: Read-only file system
            Host and machine ids are equal (fe21229597a3492b99cbdd9d8ef86f86): refusing to link journals
            Failed to synchronize cache for repo 'rhel-8-for-x86_64-highavailability-rpms', ignoring this repo.
            Failed to synchronize cache for repo 'rhel-8-for-x86_64-appstream-rpms', ignoring this repo.
            Failed to synchronize cache for repo 'rhel-8-for-x86_64-baseos-rpms', ignoring this repo.
            Failed to synchronize cache for repo 'satellite-maintenance-6.11-for-rhel-8-x86_64-rpms', ignoring this repo.
            Failed to synchronize cache for repo 'satellite-6.11-for-rhel-8-x86_64-rpms', ignoring this repo.
            Error: Unable to find a match: dnf dnf-command(config-manager)