Add junit reporting for e2e tests

[ccremer]

Summary

• Bats supports formatting tests with junit, and there's a cool junit GH action, so let's marry them!
• On successful runs, the reports may be added to the "Lint" workflow suite. This is a bug by GitHub and just of a cosmetic nature.

An example of a failing test can be found here: https://github.com/vshn/k8up/pull/259/checks?check_run_id=1651595468

Checklist

• Keep pull requests small so they can be easily reviewed.
• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking,
  as they show up in the changelog
• Update tests.