Configure signature checking

[flozanorht]

From DanielFroehlich on slack:
It should work with the installation registry, see configs at:
https://gist.github.com/DanielFroehlich/a441f1a433128014f5d6ef3409e0e622

[flozanorht]

Track https://issues.redhat.com/browse/OCPBUGS-44695 and https://issues.redhat.com/browse/OCPBUGS-44926 for the tested and documented process for air-gapped deployment with signature checks. They are, as of today, expected to land in 4.19 and 4.18, respectively.