Install Python and Node.js in the UBI containers using pyenv and fnm

[julienp]

We don't have the full matrix of versions available for the UBI containers because we are installing from the UBI software catalog. This is problematic now that we want the default to be Nodejs 22 and Python 3.13, neither of which is available.

Instead of installing from pre-built packages, use fnm and pyenv to install the versions, similar to what we do for the kitchen-sink image.