CNG: UBI Containers - LIBDIR not defined for users who do not use our build image.

Summary

In gitlab-org/build/CNG!541 (merged) we changed the UBI Dockerfiles to use ${LIBDIR} instead of hardcoding the path(e.g. COPY scripts/lib/\* ${LIBDIR}/ruby/vendor_ruby/). The value for ${LIBDIR} comes from the ubi-builder-image so this variable will not be defined for customers who do not use our build image.

Users are currently experiencing this as problems performing backups.

Associated Repo1 Issue: https://repo1.dso.mil/dsop/gitlab/gitlab/gitlab-task-runner/-/issues/9

Steps to reproduce

Build UBI containers but do not use our builder image.