🧹 chore: use JUnit 5

[gaeljw]

🤔 What's changed?

Use JUnit 5 in our internal tests, in examples (keep JUnit 4 example though) and integration tests.

Note that because of a bug in sbt/junit5 interface, @mpkorstanje had to do a workaround in cucumber-junit-platform-engine.

⚡️ What's your motivation?

Relates to #399, deprecation of cucumber-junit module and the overall deprecation status of JUnit 4.

🏷️ What kind of change is this?

• 📖 Documentation (improvements without changing code)
• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.