Changes

debian-bullseye-jenkins: sync with buster-jenkins

Prepare to let jenkins master-builds use debian-bullseye-jenkins
instead of debian-buster-jenkins. Add almost everything from the buster
Dockerfile to the bullseye Dockerfile that is not there, except for:
dh-systemd (not available in debian11)

Also add python2, as some projects still require it to run tests
(OS#5950).

Related: OS#5949
Change-Id: I51925d0ab9e5a779379efab59c381ef12fb60929

debian-bullseye-jenkins-arm: add new container

Add a bullseye based container that can be used instead of
debian-buster-jenkins-arm. The master-builds jenkins jobs will attempt
to use this jenkins job for the arm builds after setting the main
default image from debian-buster-jenkins to debian-bullseye-jenkins.

Related: OS#5949
Change-Id: I8e1741f86ffb8abd658d1e4e0415dfd11fb1a8a1