Usage of unsupported packages

[plettich]

Ubuntu only provides 5 years support for a limited number of packages (main and restricted repositories: https://ubuntu.com/about/release-cycle). Packages from universe or multiverse only have 3 years support.
The package support status can be shown with ubuntu-support-status (ubuntu-security-status since 20.04).
We should make sure that we only use packages from main or restricted as dependencies, or we should tell people to update every 3 years.