WIP: Pull the scripts from the package-source-builder repo

Move here the scripts currently embedded in the apertis-package-source-builder/overlay/usr/bin/ folder of the apertis-docker-images> repository so we collect them all in a single place:

• apertis-pkg-merge-updates
• apertis-pkg-merge-upstream-to-downstreams
• apertis-pkg-pull-updates
• ci-buildpackage
• ci-license-scan
• ci-obs-upload
• deb-git-version-gen
• osc-setup
• tally-revision

See also apertis-docker-images!88 (closed)