Show percentages as an image

[uhafner]

Downstream PR to https://github.com/uhafner/autograding-model/pull/295.

[github-actions[bot]]

• :vertical_traffic_light: JUnit - 90 of 100: 2 tests failed, 4 passed
• :footprints: JaCoCo - 0 of 100: 0% coverage achieved
• :microscope: PIT - 0 of 100: 0% mutations killed

• :warning: Warnings - 100 of 100: No warnings found

  :construction: Error Messages

  Errors:
  No matching report files found when using pattern '**/target/site/jacoco/jacoco.xml'! Configuration error for 'Line Coverage'?
  No matching report files found when using pattern '**/target/site/jacoco/jacoco.xml'! Configuration error for 'Branch Coverage'?
  No matching report files found when using pattern '**/target/pit-reports/mutations.xml'! Configuration error for 'Mutation Coverage'?
  No matching report files found when using pattern '**/target/checkstyle-result.xml'! Configuration error for 'CheckStyle'?
  No matching report files found when using pattern '**/target/pmd.xml'! Configuration error for 'PMD'?
  No matching report files found when using pattern '**/target/spotbugsXml.xml'! Configuration error for 'SpotBugs'?

  More details are available in the GitHub Checks Result.