Add GitHub Actions workflow step to add summary for test-runner results

[sanderploegsma]

The GitHub Actions workflow that runs the tests using the Java test runner currently doesn't provide very useful output (example). We can look into creating a custom action step to create a job summary from the JSON output, perhaps using actions/github-script.

This step should then at least provide:

• A job summary containing the name/slug of each tested exercise, with a total pass/fail count per exercise. Perhaps using a summary table.
• The .tests[].message for each failed test in each test-runner JSON file, perhaps by using annotations.
• The .message for each test-runner JSON file with status error, perhaps also by using annotations.

[sanderploegsma]

I once played around with creating a custom GitHub Action to make running tests using a track's test runner reusable. This was never finished but it also created job summaries so perhaps we can take that as inspiration. Here's an example: https://github.com/sanderploegsma/exercism-test-runner-action/actions/runs/6881871576

[altinocoelho]

@sanderploegsma I would like to help with this one