add junitreports for pytests

Context

This MR makes the pytest integration tests produce junit reports and upload them as artifacts to the CI. This enables an overview on the test results on the MR page. A major improvement is that the result of tests batched in a single job are more easily inspected (no need to read the log to find out which of the tests in the job failed). See here for more details.

Manually testing the MR

Check out how this MR page looks (you should see a report from the test suite on this page). You can create a spinoff branch, add a failing test, then make an MR and see how that looks.

Checklist

NA:

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.