Review CTA CI workflow

The current CI workflow is complex and not very flexible.
The Kubernetes environment is setup with cumbersome commands and not in a "standard" way.
The current CI does not allow to run parallels pipelines with different software environments.
By example it would be good to be able to test the same code with (most urgent first):

1. xrootd5
2. eos5
3. Alma9
4. Custom dev environment (by example with the new postgres library)

This is a prerequisite before adding new type of tests to the CI, so avoid doing them twice.