Build arm64 variant of docker image as part of CD

[solvingj]

• Buildx is already used in the workflow enabling multi-platform builds
• Should resolve issues for users trying to work with the image on ARM (eg. all modern macOS)
• For example, got this error:

InvalidBaseImagePlatform: Base image jenkins/jenkinsfile-runner was pulled with platform "linux/amd64", expected "linux/arm64" for current build (line 1)

Testing done

Was able to run clone the repo and run these command locally on an ARM Mac to make it work:

docker buildx build -t jenkins/jenkinsfile-runner:build-mvncache -f packaging/docker/build-mvncache/Dockerfile .
docker buildx build -t jenkins/jenkinsfile-runner -f packaging/docker/unix/eclipse-temurin-11-jre/Dockerfile .

Thats by no means a complete test, but I'm not sure if there's any reasonable way to test this in the Github Action prior to merge.

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 demonstrate the feature works or the issue is fixed

[oleg-nenashev]

Thanks! Let's see whether it works