Introduce 3.14 and drop 3.9 Python image generation

Python pre-releases

• Use rc tag, unstable Python version
• Introduce with gcc and libffi-dev installed in the meantime

Python stable release

• Remove gcc and libffi-dev once no longer necessary, once Py3.14 wheels are provided to run poetry install
• Remove rc tag once Python 3.14 is released as stable
• Drop Python 3.9 image generation

Post

• Create follow-up ticket for Py 3.15/3.10