allow defining multiple values files

Summary

• for larger integration tests
• separately for publishing

I am inclined to make integration this with a bot creating MRs. And selecting if larger test sets are run with labels.

Scheduled pipelines is another option, useful in some cases, like for the combinations which are not meant to be merged.

But its easier to maintain centralized bot than a combination of scheduled pipelines, I think. And also MRs can be merged after they pass, regularly updating repository with their dependencies.

/cc @mlinhoff