chore(Jenkinsfile) Use jenkins/ath instead of rebuilding it

[dduportal]

Fixes #988

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[timja]

Nice!

It's switched from previously a consistent range of
2m50 to 3m building the image

to
1m to 1m 10 pulling the image.

Further optimisation could be done to pre-pull the image to the VM image or use a container registry local to the cloud provider I suspect, but for now that's a lot better

[basil]

But does this not use the last published version of the image rather than the one defined in code under test? That is not OK from a correctness perspective, because that means a change to the image made in a PR (the code under test) will not take effect in that PR. This also makes it impossible to change both the image and the consumer of the image in the same PR, which was possible before this. A better approach from a correctness perspective would be to build the image from the code under test once and then consume it from each parallel branch.

[basil]

Causes #1193