[CI] Move CI setup into it's own repo

I've tried having replicating the setup to all modules and syncing them, but that just does not scale really.

• Create repo https://zivgitlab.uni-muenster.de/HPC2SE-Project/pacxx-ci, take over setup from pacxx-runtime (pacxx-ci@85d04511, https://zivgitlab.uni-muenster.de/HPC2SE-Project/pacxx-ci/pipelines/5431)
• Update https://zivgitlab.uni-muenster.de/HPC2SE-Project/pacxx-runtime (!42 (merged))
• Update the other repos
  • https://zivgitlab.uni-muenster.de/HPC2SE-Project/pacxx-llvm2 (pacxx-llvm2!13 (merged))
  • https://zivgitlab.uni-muenster.de/HPC2SE-Project/pacxx-rv2 (pacxx-rv2!12 (merged))
  • https://zivgitlab.uni-muenster.de/HPC2SE-Project/pacxx-clang (pacxx-clang!10 (merged))
  • https://zivgitlab.uni-muenster.de/HPC2SE-Project/pacxx-samples (pacxx-samples!35 (merged))