feat(platforms): Adds s390x, ppc64le and armv7 architectures

[gounthar]

After discussing with @ksalerno99 yesterday during the Platform SIG meeting, I considered that adding support for a few platforms for JDK21 would be beneficial.

I then propose to add "linux/s390x", "linux/ppc64le" and "linux/arm/v7" as new target platforms for our JDK21 preview images.

I have also updated the bookworm tag and the JDK build number, as they are not yet tracked with updatecli.

Testing done

docker buildx bake --file docker-bake.hcl debian_slim_jdk21
docker buildx bake --file docker-bake.hcl debian_jdk21

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]

have you checked this is still needed on 21?

[gounthar]

Yes. If you know of a trick with qemu to get rid of that, please let me know.