Fixing issues with postgresql16-contrib

What is your Merge about?

Multiple variable and naming issues caused the installation to install postgresql16-server instead of postgresql16-contrib as indicated in the build-amd64 job: https://repo1.dso.mil/dsop/security-compass/sd-elements/common-init/-/jobs/44009895#L950

I don't think this needs a version bump, but please let me know otherwise.