Fix Package::supportedUntil never getting the date

Summary:
We were expecting to find a Release file, but package archives have
moved from Release files to InRelease files, which have inlined GPG
signature.

Moreover, we try to get the release date from distro-info/ubuntu.csv and prefer it over the [In]Release file.
We get the release Id and Codename from /etc/os-release, which is more modern than lsb-release.

Reviewers: sitter

Reviewed By: sitter

Differential Revision: https://phabricator.kde.org/D13662