Resolve "Upgrade testing image to Ubuntu 22.04"

This MR upgrades the Utopia testing image to Ubuntu 22.04 (Jammy Jellyfish) and uses gcc-11 instead of gcc-10.

Is there something that needs to be double checked?

• Upgrade to gcc-11 ok? Or should we rather go with gcc-12?
• Documentation ok?

Can this MR be accepted?

• Implemented the changes
  • Updated docker image
  • ... and pushed under its own tag, ccees/utopia-base:jammy-v2.1, to docker hub, keeping the version scheme
  • Updated CI/CD
• Added or extended tests Tests should remain the same
  • … and still work, as tested in this pipeline
• Added or updated documentation (in README)
  • Which Ubuntu version is used
  • Updated table of tested versions
• Reasonably up-to-date with current master
• Pipeline passing without warnings
• Squash option set
• Docker hub page updated
• Reviewed and approved

Related issues

Closes #350 (closed)