Switch to CERN CentOS stream 8 as base for x86 and arm64 images

Motivation:

• We want to be able to access mounted AFS & EOS directories when using the algo & slice test runner images.
• From tests on a VM at CERN (CS8 with podman), this is possible for:
  • cern/cc7-base:20220401-1
  • cern/c8-base:20211201-1
  • cern/cs8-base:20211201-1
• Due to early end-of-life for CentOS8, there were no new tags for cern/c8-base in 2022
• The cern/cc7-base is only built for x86, whereas cern/c8-base and cern/cs8-base are built for both x86 and arm64.
• Given that no new boards have armv7 Zynqs, eventually we should only need images for x86 and arm64, so switching both x86 and arm64 images to cern/cs8-base seems like the best bet for now.

Example command used for tests:

podman --root /tmp/${USER}/containers run --rm --userns keep-id -v /tmp/krb5cc_${UID}:/tmp/krb5cc_${UID}:ro -v /eos:/eos -v /afs:/afs -it docker.io/cern/cs8-base:20220401-1 ls -al /eos/user/t/tsw /afs/cern.ch/user/t/tsw/cms-phase2