kubevirt/virt-cdi-importer: improper TLS certificate validation

Kubevirt/virt-cdi-importer, versions 1.4.0 to 1.5.3 inclusive, were reported to disable TLS certificate validation when importing data into PVCs from container registries. This could enable man-in-the-middle attacks between a container registry and the virt-cdi-component, leading to possible undetected tampering of trusted container image content.