Sometime the main server of snapshot.debian.org is not sync
which block us from downloading new packages from Debian.
Thus to avoid depending on a single server add a mirror
as fallback.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

Updates from *-proposed-updates repositories are not pulled anymore
by default because it can contain undesirable updates for Apertis.
However, we still want updates from *-updates repositories instead.

"proposed-updates" contains updates not officialy part of Debian
contrary to "updates".

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

The Apertis pipeline imports backport and/or proposed-updates versions
by default, this is not needed and leads to miss some security updates.
Because, importing versions from backports and proposed-updates is not
part of our standard workflow, this should only be optional to avoid
confusing the pipeline.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

We may want to run the CI pipeline to pull updates from a debian release
backports upstream. Extend this script to handle those branches.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>

Updates available in -security and -proposed-updates fall into the main Debian repository
after a Debian release point. In case an update has been imported from -security or -proposed-updates,
our main Debian branch stays out of date. Consequently, the Dashboard wrongly complains about an
available update from Debian.

In this scenario, the main Debian branch needs to be synchronized with the
-security or -proposed-updates branch used previously.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

These tools are moved from
`infrastructure/apertis-docker-images/package-source-builder`.

Signed-off-by: Frédéric Danis <frederic.danis@collabora.com>