As of late, we've seen more and more errors related to Elastic's container registry not being reachable, preventing us from retrieving a container image. Something like this:

https://ci.hibernate.org/blue/organizations/jenkins/hibernate-search/detail/PR-2587/28/pipeline

They seem to mirror their container images to dockerhub, so let's switch to dockerhub? That will require removing the docker.elastic.co/ prefix in the image name, and adding an authenticed pull of the image before we run builds on CI.

While we're at it, we could move the names/tags of container images to a separate properties file, sourced both from the POM and from the CI job, so that we only have one place where we keep that information up to date.