Refactor code around compute_{common,local}_version.py

[marbre]

As soon as #19034 lands, build_tools/python_deploy/compute_common_version.py and build_tools/python_deploy/compute_local_version.py are used in the workflows .github/workflows/oneshot_candidate_release.yml and .github/workflows/schedule_candidate_release.yml to compute the version numbers. Each script execution prints a computed version number which is temporarily saved in a bash variable and passed to $GITHUB_ENV , for example:

package_version="$(python3 build_tools/python_deploy/compute_common_version.py -rc)"
echo "package_version=${package_version}" >> $GITHUB_ENV

Parts of this bash scripting should be moved to Python scripts, that allow to freely log and write outputs all in a single process and without needing to juggle between bash and Python. The script could detect if it is being run locally or on CI by the presence of $GITHUB_ENV and log what it would do on GitHub if you run it locally. If run on CI, the script should set variables accordingly. See https://stackoverflow.com/a/70123641 for tips on writing to $GITHUB_ENV from Python.

Also see the original discussion started with #19034 (comment) as well as comment #19034 (comment).