Prepend tag with Python package name if multiple packages are defined

[krassowski]

This aims to alleviate https://github.com/jupyter-server/jupyter_releaser/issues/567#issuecomment-2067274319 by checking for package-specific tags. As of today it effectively, skips the check for already existing tags when:

• package names are defined for python packages, and
• there is more than one python package

It does not implement creating tags per Python package yet.