Adding s390x support to solr-operator docker image

Hi,
I could successfully build the solr-operator image for s390x and deploy the solr operator pod on s390x without doing any code changes.
The docker hub image of [solr-operator](https://hub.docker.com/r/apache/solr-operator/tags?page=1&ordering=last_updated) currently supports only amd64 and arm64.
Can we make this image support s390x as well?

Start by reviewing the solr-operator image build and publishing configuration associated with the Docker Hub tags, then compare the existing amd64 and arm64 targets with the reported s390x build. Done means the published solr-operator image includes an s390x variant and can be deployed as an operator pod on s390x.

Written by the indexing model from the issue text.