maven.gitlab-ci.yml - review script used to lookup deploy tokens and whether it can be simplified by using a default token

The approach currently used in maven.gitlab-ci.yml to look up a GitLab Deploy Token was originally lifted from existing HR projects and involves calling GCP Secrets Manager apis to retrieve the tokens.

By default GitLab Project Factory managed tokens already have a Deploy Token created by default, ${env.CI_JOB_TOKEN that already has permission publish to the project's parent group Package Registry.

Review existing HR projects to evaluate whether the lengthy .maven.get_tokens script can be replaced with use of the default deploy token instead.