Implement code coverage

[ekohl]

I wonder how we could nicely implement that in https://github.com/theforeman/actions/

The following details need to be considered:

• we run the tests as a matrix (each branch tests something else, test:$plugin, db:seed, etc), so we'd need unique artifact names somehow
• the path each plugin wants to archive might be different

My current idea is:

• have an input artifact_path, which gets passed 1:1 to actions/upload-artifact
• only execute the step if artifact_path is actually defined AND the task is test:$plugin, so it runs only once

That would allow us to have a stable simple artifact name (test_artifacts or $plugin_artifacts) and allow other steps to consume that again.

Originally posted by @evgeni in theforeman/foreman_fog_proxmox#311 (comment)