This adds a POOLAPI variable to make the pipe commands shorter and
more readable, and removes the unused job outputs feature (originally
intended to store the git commit outcome and conditionally trigger
another workflow, but its usage was commented out because we could not
get it to work as intended).
Temporary files are written into .cache instead of /tmp (the .cache is
also something that the code from pool-publication-page may use for
its own purposes).
