due to recent DC move, and different set of IP addresses, we can't rsync SIG content to internal mirror in the stream infra

It's needed to upgrade packages in stream infra, so instead of pulling all SIGs content, we'll just use a "hot cache" on a nginx vhost

It's already needed as the ppc64le infra hosts can't be upgraded for the Virt SIG ppc64le kvm-host feature (and packages)