Add template-python3.12 flavor

[tomuben]

Background

We need to prepare a new flavor for Python3.12, based on Ubuntu 24.04. Initial test was already done in branch: python12_tmp.
A few things which need to be fixed:

1. Upgrade to pip 0.24 requires to use flag --break-system-packages. If we use this flag in installer scripts: Or we have to switch to pip 0.24 in all flavors or we need to stick onto old pip version or we have to pass this flag to the scripts
2. Python package imp was removed from Python3.12 (see

• https://docs.python.org/3/library/importlib.html#importlib.util.module_from_spec
• https://docs.python.org/3.11/library/imp.html
• https://stackoverflow.com/questions/32175693/python-importlibs-analogue-for-imp-new-module