fix: Override dh_installdeb to overwrite auto-generated conffiles

[jacobgkau]

Fixes pop-os/upgrade#319.

The standard dh_installdeb takes our pop-default-settings.conffiles list and adds its auto-detected conffiles (anything under /etc) to that list. We need to override that by copying our list back over the generated one in order to prevent important files like /etc/os-release and /etc/lsb-release (which we package as /etc/pop-os/os-release and /etc/pop-os/lsb-release) from being declared as conffiles (which means they don't get updated by automated utilities like pop-upgrade).

For QA, note that if you're testing this on a system affected by the bug (running Jammy but showing a different release name in /etc/os-release), you'll need to correct the suite for the staging repository after adding it, because apt-manage will add it based on what's in /etc/os-release//etc/lsb-release.

[mmstick]

Seems odd that installdeb isn't automatically doing this, but if it works it works.

[jacobgkau]

Seems odd that installdeb isn't automatically doing this,

I think installdeb is behaving as described by the documentation: https://www.debian.org/doc/manuals/maint-guide/dother.en.html#conffiles

dh_installdeb(1) automatically flags any files under the /etc directory as conffiles,

That's why we have to overwrite the list that it's creating, to effectively remove those /etc/pop-os/... entries that aren't actually conffiles.