to avoid deleting spack submodule when updating persistent installations

Eric Müller authored 3 months ago and Eleni Mathioulaki committed 1 month ago

This introduces a submodule for yashchiki.

We need to check if the flexibility of the script is actually needed.
(And how this ever could have worked with a moving target spack ;).)

(but continue using the old image for OKD CSCS build jobs)