Docker fully qualified image names (#15689)

* Fully qualified docker image names for the main Dockerfile and Complement related.

* Fully qualified docker image names for Dockerfiles associated with building Debian release artifacts.

This one is harder and is separate from the other commit in case it wasn't correct or was unwanted. I decided to
do the expansion on the docker images in the Dockerfile itself, instead of the various source places that build
which distribution that is selected, as it would have been more invasive with the scripts breaking up the string
for tagging and such. This one is untested.

* Changelog

* Update docker/Dockerfile-workers

* Update docker/complement/Dockerfile

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Co-authored-by: reivilibre <olivier@librepush.net>

scripts-dev/build_debian_packages.py

@@ -20,6 +20,8 @@ from concurrent.futures import ThreadPoolExecutor
 from types import FrameType
 from typing import Collection, Optional, Sequence, Set
 
+# These are expanded inside the dockerfile to be a fully qualified image name.
+# e.g. docker.io/library/debian:bullseye
 DISTS = (
     "debian:buster",  # oldstable: EOL 2022-08
     "debian:bullseye",