Add multiarch support for test image

[mkralik3]

• Added support for multiarch

docker buildx create --use --platform linux/amd64,linux/arm64,linux/ppc64le,linux/s390x
docker buildx build --push --platform linux/amd64,linux/arm64,linux/ppc64le,linux/s390x --tag quay.io/maistra/maistra-test-tool:2.6_multi .

• Updated workflow to build multiarch image
  • Example of success build on my fork: https://github.com/mkralik3/maistra-test-tool/actions/runs/10557570439
  • Image: https://quay.io/repository/mkralik3/maistra-test-tool?tab=tags

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all