Python support

Changes introduced

Due to ongoing cleanup of runners https://cern.service-now.com/service-portal?id=outage&n=OTG0078219 python wasn't working in the new runners that have python3.

Changing the script to use python3 instead of python would also work in the new default runners tags: k8s-cvmfs but I put here a specific image.

This might have to be rethought when the change to the new runners is complete.

Tests

Failing pipelines pass

Issues resolved

Closes #