NEXUS-42724 add base image reference redhat jobs

[codetreras]

This PR introduces a new label inside the Docker Image published on the RedHat catalog. It is a continuation of a https://github.com/sonatype/docker-nexus3/pull/180 that is already merged that introduced the same changes for internal images and images published in Docker Hub.

This pull request makes the following changes:

It changes the Jenkins job used to publish Nexus images to the RedHat Catalog in order to add the logic for obtaining the base image reference link. It changes the scripts associated to such job to include the base image reference link as a label called base-image-ref.

It relates to the following issue:

JIRA: https://sonatype.atlassian.net/browse/NEXUS-42724