Add timestamp to JUnit reporter

[evrom]

🤔 What's changed?

Adds a timestamp of the start time of the testsuite to the JUnit reporter

⚡️ What's your motivation?

Fixes cucumber/junit-xml-formatter#44

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• 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.

---

This text was originally generated from a template, then edited by hand. You can modify the template here.

[coveralls]

coverage: 97.806% (-0.03%) from 97.838%
when pulling 734ac6d on evrom:add-timestamp-to-junit-report
into ddf424a on cucumber:main.

[davidjgoss]

Thanks again for doing this @evrom. Closing this is the request has been picked up in the new formatter here cucumber/junit-xml-formatter#45