Rebase LTS/ELTS changes on top of the Salsa CI's pipeline as of 2024-04-30

This MR overrides !12 (closed) (and !14 (closed) (gitlab doesn't allow to change source branche in MR, so creating a new MR because there have been changes in upstream pipeline, and I prefer to keep things consistent))

My goal with this MR is to simplify and squash the commits, keeping in mind to parts of code that could be merged upstream.

I gave up the idea of doing a "clean" rebase, as it was my goal with !12 (closed) (we are "88 commits behind, 118 commits ahead"). It is too complex and we don't gain too much. I haven't been able to finish that since last November, so just let's make it simple. We need to import some changes from upstream to fix long-standing issues in our fork.